Document:

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                                                                   Exhibit 10.16

                                AGREEMENT OF SALE

                                   DATED AS OF
                               NOVEMBER 10, 2005,

                                 BY AND BETWEEN

                     CARFAX ENTERPRISES LIMITED PARTNERSHIP

                                       AND

                           COLUMBIA EQUITY TRUST, INC.

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                                TABLE OF CONTENTS

<TABLE>
<S>                                                                           <C>
1.  Agreement to Sell and Purchase.........................................    1
2.  Price and Payment......................................................    2
3.  Closing................................................................    3
4.  Condition of Properties and Title......................................    3
5.  Survey.................................................................    5
6.  Conditions to Closing..................................................    6
    (a) Purchaser's Conditions.............................................    6
    (b) Seller's Conditions................................................    9
    (c) Conditions Generally...............................................   10
    (d) Closing Delivery Covenants.........................................   10
7.  Seller's Representations...............................................   11
    (a) Representations....................................................   11
    (b) Limitations on Seller's Representations and Warranties.............   15
    (c) No Other Representations or Warranties.............................   15
    (d) Seller's Knowledge.................................................   16
8.  Purchaser's Representations............................................   16
    (a) Representations....................................................   16
    (b) Purchaser's Knowledge..............................................   17
9.  Covenants..............................................................   17
    (a) Covenants of Seller................................................   17
    (b) Covenants of Purchaser.............................................   18
10. Apportionments.........................................................   18
11. Closing Matters........................................................   21
    (a) Payment of Recording, Title, and Other Fees........................   21
    (b) Transfer of Utilities..............................................   22
12. Study Period...........................................................   22
    (a) Length of Study Period.............................................   22
    (b) Purchaser's Termination............................................   23
    (c) Due Diligence Indemnity............................................   23
</TABLE>

<PAGE>

<TABLE>
<S>                                                                           <C>
    (d) Additional Inspection..............................................   24
    (e) Review of Contracts................................................   24
13. Risk of Loss...........................................................   24
    (a) Destruction or Damage Prior to Closing.............................   24
    (c) Condemnation.......................................................   25
14. Brokerage..............................................................   26
15. Failure to Close.......................................................   26
    (a) Purchaser's Default................................................   26
    (b) Seller's Default...................................................   27
16. Notices................................................................   27
17. Choice of Law..........................................................   28
18. Indemnification Generally..............................................   28
    (a) Seller's Indemnification...........................................   29
    (b) Purchaser's Indemnification........................................   29
    (c) Scope of Indemnification...........................................   29
    (d) Procedures for Indemnification.....................................   29
19. Survival...............................................................   29
20. Miscellaneous..........................................................   30
    (a) Entire Agreement; Exhibits.........................................   30
    (b) Amendments.........................................................   30
    (c) Press Releases.....................................................   30
    (d) Binding Effect.....................................................   30
    (e) Partial Invalidity.................................................   30
    (f) Recordation of Agreement...........................................   30
    (g) Prevailing Party Costs.............................................   31
    (h) Headings; Section, Exhibit and Schedule References.................   31
    (i) Counterparts.......................................................   31
    (j) Assignment.........................................................   31
    (k) No Waiver..........................................................   31
    (l) No Other Parties...................................................   31
    (m) Certain Definitions................................................   31
    (n) Time of the Essence................................................   32
    (o) Business Days......................................................   32
    (p) Execution by Facsimile.............................................   32
21. Escrow Provisions......................................................   31
</TABLE>

                                       ii
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                                AGREEMENT OF SALE

     THIS AGREEMENT OF SALE (the "Agreement") is made, and is intended to be
effective, as of November 10, 2005 (the "Effective Date"), by and between CARFAX
ENTERPRISES LIMITED PARTNERSHIP, a Delaware limited partnership ("Seller"), and
COLUMBIA EQUITY TRUST, INC., a Maryland corporation (or its permitted assignee
in accordance with this Agreement)("Purchaser").

                                    RECITALS:

     R-1. Seller is the owner of that certain improved real property located at
and known as 10467 White Granite Drive, Oakton, Virginia 22124, as identified
more particularly in Exhibit A-1 attached hereto and made a part hereof (the
"Oakton Property").

     R-2. Seller is the owner of that certain improved real property located at
and known as 625 Slaters Lane, Alexandria, VA 22314, as identified more
particularly in Exhibit A-2 attached hereto and made a part hereof (the
"Towngate Property").

     R-3. Seller desires to sell the Oakton Property and the Towngate Property
to Purchaser, and Purchaser desires to purchase the Oakton Property and the
Towngate Property from Seller, subject to and in accordance with all of the
terms and provisions of this Agreement.

     NOW, THEREFORE, in consideration of the mutual covenants and provisions
contained herein, and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereby agree as
follows:

     1. AGREEMENT TO SELL AND PURCHASE. Purchaser agrees to purchase from
Seller, and Seller agrees to sell and convey to Purchaser, in accordance with
all of the terms and conditions specified in this Agreement, the following:

          (A) the Oakton Property together with (i) any and all improvements,
appurtenances, rights, privileges, and easements benefiting, belonging or
pertaining to the Oakton Property; (ii) any right, title, and interest of Seller
in and to any land lying in the bed of any street, road, or highway or other
right-of-way, whether existing or proposed, in front of or adjoining the Oakton
Property; (iii) all of Seller's right, title and interest in and to fixtures
used in connection with the operation of the improvements on the Oakton Property
and located therein, including without limitation any of the following: boilers,
pumps, tanks, electric panel switchboards, lighting equipment and wiring,
heating, plumbing, ventilating and air conditioning apparatus and equipment,
elevators, escalators, and conveyors; (iv) all other tangible personal property
owned by Seller and located and used at the Oakton Property, including all
security and alarm systems, cables, conduits, and telecommunication facilities
servicing the Oakton Property (except for such personal property, if any,
maintained on the Oakton Property by ELV Associates, Inc.); (v) all transferable
licenses and warranties, if any; and (vi) the "Oakton Leases" (as defined in
Section 7(viii) hereof (collectively, the "Oakton Property"); and

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          (B) the Towngate Property together with (i) any and all improvements,
appurtenances, rights, privileges, and easements benefiting, belonging or
pertaining to the Towngate Property; (ii) any right, title, and interest of
Seller in and to any land lying in the bed of any street, road, or highway or
other right-of-way, whether existing or proposed, in front of or adjoining the
Towngate Property; (iii) all of Seller's right, title and interest in and to
fixtures used in connection with the operation of the improvements on the
Towngate Property and located therein, including without limitation any of the
following: boilers, pumps, tanks, electric panel switchboards, lighting
equipment and wiring, heating, plumbing, ventilating and air conditioning
apparatus and equipment, elevators, escalators, and conveyors; (iv) all other
tangible personal property owned by Seller and located and used at the Towngate
Property, including all security and alarm systems, cables, conduits, and
telecommunication facilities servicing the Towngate Property (except for such
personal property, if any, maintained on the Towngate Property by ELV
Associates, Inc.); (v) all transferable licenses and warranties, if any; and
(vi) the "Towngate Leases" (as defined in Section 7(viii) hereof) (collectively,
the "Towngate Property") (the Oakton Property and the Towngate Property are
hereinafter sometimes referred to, collectively, as the "Properties").

     2. PRICE AND PAYMENT. The aggregate purchase price for the Properties shall
be the sum of TWENTY-SIX MILLION EIGHT HUNDRED FIFTY THOUSAND AND 00/100 DOLLARS
($26,850,000.00) (the "Purchase Price"). For purposes of tax reporting only, the
Purchase Price shall be allocated between the Properties as follows: SIXTEEN
MILLION ONE HUNDRED FIFTY THOUSAND AND 00/100 DOLLARS ($16,150,000.00) as and
for the purchase price for the Oakton Property, and TEN MILLION SEVEN HUNDRED
THOUSAND AND 00/100 DOLLARS ($10,700,000.00) as and for the purchase price for
the Towngate Property. The Purchase Price shall be payable as follows:

          (A) (i) Not later than 5:00 o'clock p.m. (local Virginia time) on the
second business day following the full execution of this Agreement by Seller and
Purchaser, Purchaser shall deliver, or cause to be delivered, the sum of TWO
HUNDRED THOUSAND AND 00/100 DOLLARS ($200,000.00) (the "Initial Deposit"), by
wire transfer of immediately available federal funds actually received, to
Commercial Title Group, 8605 Westwood Center Drive, Suite 200, Vienna, Virginia
22182 (the "Escrow Agent" or the "Settlement Agent").

               (ii) On condition that this Agreement is not terminated by
Purchaser in accordance with Section 12 hereof, Purchaser, not later than 5:00
o'clock p.m. (local Virginia time) on the second business day following the
Study Period Termination Date (as defined in Section 12(a) hereof), shall
increase the Initial Deposit to ONE MILLION AND 00/100 DOLLARS ($1,000,000.00)
by delivering to the Escrow Agent an additional deposit (the "Additional
Deposit") in the amount of EIGHT HUNDRED THOUSAND AND 00/100 DOLLARS
($800,000.00), in the form of immediately available federal funds actually
received (the Initial Deposit and the Additional Deposit being hereinafter
referred to as the "Deposit").

               (iii) If Purchaser exercises its option to extend the Closing
Date for up to an additional thirty (30) days in accordance with Section 3
hereof, then Purchaser, not later than 5:00 o'clock p.m. (local Virginia time)
on the second business day following the "Closing Extension Date" as defined in
Section 3 hereof, shall increase the Deposit to ONE MILLION

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FIVE HUNDRED THOUSAND AND 00/100 DOLLARS ($1,500,000.00) by delivering to the
Escrow Agent an additional deposit (the "Extension Deposit") in the amount of
FIVE HUNDRED THOUSAND AND 00/100 DOLLARS ($500,000.00), in the form of
immediately available federal funds actually received (the Deposit and the
Extension Deposit being hereinafter referred to as the "Deposit").

               (iv) On condition that this Agreement is not terminated by
Purchaser in accordance with Section 12 hereof, the Deposit shall be
non-refundable, except as specifically provided for in Section 15(b) hereof or
elsewhere in this Agreement.

               (v) The Settlement Agent shall hold any and all deposits received
under this Section 2 in escrow in accordance with and pursuant to the provisions
of Section 21 hereof. For the purposes of the interest-bearing account specified
in Section 21, Purchaser's tax identification number is set forth below
Purchaser's signature hereto.

          (B) The balance of the Purchase Price (the "Purchase Price Balance"),
after taking into account the applicable Deposit under and pursuant to this
Section 2, and subject to prorations and adjustments as provided for in this
Agreement, shall be paid by Purchaser at "Closing" (as hereinafter defined) by
wire transfer of immediately available federal funds actually received and
credited to the account of the Settlement Agent to be designated by it in
writing prior to Closing.

     3. CLOSING. Subject to the other applicable provisions of this Agreement
and to the immediately succeeding sentence, closing of the transactions
contemplated hereby (the "Closing") shall occur at the offices of the Settlement
Agent at 10:00 a.m. on the tenth (10th) business day following the Study Period
Termination Date as defined in Section 12 hereof, or if that day is not a
business day, then on the immediately succeeding business day, or on such other
day, or at such other time or place as may be otherwise agreed upon by Seller
and Purchaser in their respective sole discretion. Purchaser shall have the
option to extend the date for the Closing for up to a maximum period of thirty
(30) days provided that and on specific condition that Purchaser (a) delivers to
Seller on a date (the "Closing Extension Date") not later than three (3)
business days prior to the originally scheduled date for Closing a written
notice exercising such option and specifying the new date for Closing, and (b)
delivers to the Escrow Agent on or before the Closing Extension Date the
Extension Deposit in accordance with Section 2 hereof. The term "Closing Date,"
as used in this Agreement, shall mean the date when the transactions
contemplated hereunder are consummated.

     4. CONDITION OF PROPERTIES AND TITLE.

          (A) Purchaser shall purchase each of the Oakton Property and the
Towngate Property in its present "AS IS, WHERE IS, WITH ALL FAULTS" condition,
subject to the reasonable and ordinary wear and tear of the Oakton Property and
the Towngate Property, as applicable, between the Effective Date and the Closing
Date, and to the other applicable provisions of this Agreement.

                                       3

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          (B) Title to each of the Oakton Property and the Towngate Property to
be conveyed to Purchaser shall be fee simple title, good and clear of record and
in fact, and marketable, and shall be insurable on, and a recognized title
insurance company licensed to do business in the Commonwealth of Virginia and
reasonably acceptable to Purchaser (the "Title Company") shall be willing to
issue, an ALTA standard full coverage form owner's commercial title insurance
policy with all endorsements reasonably requested by Purchaser (the "Title
Policy") at standard premium rates; subject, however, to those matters (if any)
affecting title to the Oakton Property or the Towngate Property, as may be
applicable, that are set forth in Schedule B to the "Title Commitment" (as
hereinafter defined) related to the Oakton Property or the Towngate Property, as
may be applicable, and accepted by Purchaser in accordance with this Section 4.

          (C) (i) Purchaser, at its sole expense, promptly shall order from the
Title Company an ALTA standard full coverage commitment for owner's title
insurance for each of the Oakton Property and the Towngate Property (each, a
"Title Commitment"), together with copies of all documents and instruments
affecting title to the Oakton Property or the Towngate Property, as may be
applicable, and otherwise mentioned in the Title Commitment.

               (ii) If Purchaser determines, in its sole discretion, that title
to either of the Oakton Property or the Towngate Property is not satisfactory,
then Purchaser promptly shall deliver written notification of such determination
(the "Disapproved Title Matters") to Seller on or prior to the Study Period
Termination Date. If Purchaser does not deliver written notice of the
Disapproved Title Matters to Seller on or prior to the Study Period Termination
Date, then Purchaser shall be deemed to have approved the state of the title to
the Oakton Property and the Towngate Property, and to have received from the
Title Company a Title Commitment for each of the Oakton Property and the
Towngate Property, including all endorsements thereto, as required under this
Section 4, and Purchaser shall not have any further right to object to the
condition of title to either the Oakton Property or the Towngate Property.

               (iii) If Seller receives written notice from Purchaser of the
Disapproved Title Matters on or prior to the Study Period Termination Date in
accordance with the provisions of this Section 4, then Seller may elect by
written notice to Purchaser, within five business days after its receipt of
written notice from Purchaser of the Disapproved Title Matters, (1) to take such
actions at its own expense as are commercially reasonable (not involving
litigation) to correct the Disapproved Title Matters and Seller shall have a
period of forty-five (45) calendar days from the date of Seller's election to do
so, or (2) not to take any remedial action. If Seller fails timely to elect
either option (1) or (2), then Seller shall be deemed to have elected option (2)
above. If Seller elects option (1) above and is unable to correct the
Disapproved Title Matters within said forty-five (45) day period, then Seller
shall deliver written notice of same to Purchaser within five business days
after the expiration of said forty-five (45) period, whereupon Purchaser shall
have the right, exercisable by written notice delivered to Seller within five
business days after Purchaser's receipt of Seller's notice, (A) to terminate
this Agreement, or (B) to agree to accept both of the Properties subject to such
of the Disapproved Title Matters that Seller has been unable to correct and to
proceed promptly to Closing. If Purchaser fails timely to elect either of
options (A) or (B), then Purchaser shall be deemed to have elected option (A).
If Seller elects, or is deemed to have elected, option (2) above, then Purchaser
shall have the right

                                       4

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to elect either of options (A) or (B) above by written notice to Seller within
five business days after Purchaser's receipt of Seller's written notice of said
election (or if Seller fails to make a timely election, within three business
days after receipt of Seller's written request for Purchaser's election), and
the procedures outlined above shall apply. If Purchaser terminates or is deemed
to have terminated this Agreement in accordance with this Section, then the
Deposit and all accrued interest thereon shall be refunded to Purchaser, and no
party shall have any further rights, liabilities, or obligations in connection
with this Agreement, except for those which may arise under Section 12(c)
hereof.

               (iv) The Closing Date shall be deferred reasonably, if necessary,
to take into account the forty-five (45) day period provided to Seller in clause
(iii) above.

          (D) Notwithstanding anything in the foregoing to the contrary, any
deed of trust, mortgage, judgment lien, perfected mechanic's lien, tax lien,
security interest, financing statement, or other monetary lien against either of
the Properties (each, a "Lien") shall be removed by Seller at or prior to the
Closing, whether or not Purchaser provides written notice to Seller of such
Lien. Seller hereby authorizes the Settlement Agent to use Purchaser's funds
payable at Closing for the satisfaction and discharge of any Lien.

     5. SURVEY.

          (A) Seller and Purchaser each acknowledges and confirms that prior to
or contemporaneously with the full execution of this Agreement, Seller has
delivered to Purchaser a current certified survey of each of the Properties
(each, a "Survey", and collectively, the "Surveys") prepared by a licensed
surveyor. At Closing, Seller shall receive a credit from Purchaser in the amount
of Seven Thousand One Hundred Twenty-Nine and 00/100 Dollars ($7,129.00) as
reimbursement for the aggregate cost of the Surveys. If Purchaser determines, in
its sole discretion, that the Survey of either Property is not satisfactory,
then Purchaser promptly shall deliver written notification of such determination
(the "Disapproved Survey Matters") to Seller on or prior to Study Period
Termination Date. If Purchaser does not deliver written notice of the
Disapproved Survey Matters to Seller on or prior to the Study Period Termination
Date, then Purchaser shall be deemed to have approved the Survey for each
Property and the matters contained therein, and Purchaser shall not have any
further right to object to the Survey for either Property.

          (B) (i) If Seller receives written notice from Purchaser of the
Disapproved Survey Matters on or prior to the Study Period Termination Date in
accordance with the provisions of this Section 5, then Seller may elect by
written notice to Purchaser, within five business days after receipt of written
notice from Purchaser of the Disapproved Survey Matters, (1) to take such
actions at its own expense as are commercially reasonable (not involving
litigation) to correct the Disapproved Survey Matters and Seller shall have a
period of forty-five (45) calendar days from the date of Seller's election to do
so, or (2) not to take any remedial action. If Seller fails timely to elect
either option (1) or (2), then Seller shall be deemed to have elected option (2)
above. If Seller elects option (1) above and is unable to correct the
Disapproved Survey Matters within said forty-five (45) day period, then Seller
shall deliver written notice of same to Purchaser within five business days
after the expiration of said forty-

                                       5

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five (45) period, whereupon Purchaser shall have the right, exercisable by
written notice delivered to Seller within five business days after Purchaser's
receipt of Seller's notice, (A) to terminate this Agreement or (B) to agree to
accept both of the Properties subject to such of the Disapproved Survey Matters
that Seller has been unable to correct and to proceed promptly to Closing. If
Purchaser timely fails to elect either of options (A) or (B), then Purchaser
shall be deemed to have elected option (A). If Seller elects, or is deemed to
have elected, option (2) above, then Purchaser shall have the right to elect
either of options (A) or (B) above by written notice to Seller within five
business days after Purchaser's receipt of Seller's written notice of said
election (or if Seller fails to make a timely election, within three business
days after receipt of Seller's written request for Purchaser's election), and
the procedures outlined above shall apply. If Purchaser terminates or is deemed
to have terminated this Agreement in accordance with this Section, then the
Deposit and all accrued interest thereon shall be refunded to Purchaser, and no
party shall have any further rights, liabilities, or obligations in connection
with this Agreement, except for those which may arise under Section 12(c)
hereof.

               (ii) The Closing Date shall be deferred reasonably, if necessary,
to take into account the forty-five (45) day period provided to Seller in clause
(i) above.

     6. CONDITIONS TO CLOSING.

          (A) PURCHASER'S CONDITIONS. Purchaser's obligation to pay the Purchase
Price Balance, to accept title to each of the Properties, and otherwise to
consummate the transactions contemplated hereby shall be subject to the
satisfaction of the following conditions precedent on and as of the Closing Date
(except with respect to Section 6(a)(iv) which shall be satisfied within the
time period specified therein):

               (i) Seller shall deliver to Purchaser (or to the Settlement
Agent) on or before the Closing Date the following (collectively, "Seller's
Closing Documents"):

                    (1) a special warranty deed with respect to the Oakton
Property, in substantially the form attached hereto as Exhibit B-1 (the "Oakton
Deed"), duly executed and acknowledged by Seller;

                    (2) a special warranty deed for the Towngate Property, in
substantially the form attached hereto as Exhibit B-2 (the "Towngate Deed"),
duly executed and acknowledged by Seller;

                    (3) a bill of sale with respect to the Oakton Property, in
substantially the form attached hereto as Exhibit C-1 (the "Oakton Bill of
Sale"), duly executed and acknowledged by Seller;

                    (4) a bill of sale with respect to the Towngate Property, in
substantially the form attached hereto as Exhibit C-2 (the "Towngate Bill of
Sale"), duly executed and acknowledged by Seller;

                                       6

<PAGE>

                    (5) an assignment and assumption of leases agreement with
respect to the Oakton Property, in substantially the form attached hereto as
Exhibit D-1 (the "Oakton Lease Assignment"), duly executed and acknowledged by
Seller, transferring all of Seller's right, title and interest, as landlord, in,
to and under the Oakton Leases (as hereinafter defined), and all security
deposits made under the Oakton Leases, and providing for Purchaser's assumption
thereof and for mutual indemnities;

                    (6) an assignment and assumption of leases agreement with
respect to the Towngate Property, in substantially the form attached hereto as
Exhibit D-2 (the "Towngate Lease Assignment"), duly executed and acknowledged by
Seller, transferring all of Seller's right, title and interest, as landlord, in,
to and under the Towngate Leases (as hereinafter defined), and all security
deposits made under the Towngate Leases, and providing for Purchaser's
assumption thereof and for mutual indemnities;

                    (7) a general assignment and assumption agreement with
respect to the Oakton Property, in substantially the form attached hereto as
Exhibit E-1 ("Oakton General Assignment"), assigning to Purchaser all of
Seller's right, title and interest in and to all Oakton Contracts (as
hereinafter defined) that are assumed by Purchaser pursuant to and in accordance
with the provisions of this Agreement, and all warranties and guaranties related
to the Oakton Property, to the extent transferable, and providing for
Purchaser's assumption thereof and for mutual indemnities;

                    (8) a general assignment and assumption agreement with
respect to the Towngate Property, in substantially the form attached hereto as
Exhibit E-2 ("Towngate General Assignment"), assigning to Purchaser all of
Seller's right, title and interest in and to all Towngate Contracts (as
hereinafter defined) that are assumed by Purchaser pursuant to and in accordance
with the provisions of this Agreement, and all warranties and guaranties related
to the Towngate Property, to the extent transferable, and providing for
Purchaser's assumption thereof and for mutual indemnities;

                    (9) fully executed originals (or copies certified as true
and correct, if originals are not available) of all Oakton Leases and Towngate
Leases and Oakton Contracts and Towngate Contracts, and all rent records with
respect to current Oakton Tenants (as hereinafter defined) and Towngate Tenants
(as hereinafter defined) in the possession or under the control of Seller;

                    (10) an amount equal to the total of all tenant security
deposits under the Oakton Leases and the Towngate Leases, or, at Seller's
option, in lieu of delivery of such an amount, a credit equal to such amount
shall be allowed against the Purchase Price Balance (to the extent any deposits
are in a form other than cash, such deposits shall be transferred to Purchaser
at Closing in a manner reasonably acceptable to Purchaser);

                    (11) to the extent the same are in Seller's or Seller's
agent's possession, a complete set of keys, codes, and other security devices
for each of the Properties;

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<PAGE>

                    (12) a letter, duly executed by Seller, to each Oakton
Tenant and each Towngate Tenant (as hereinafter defined) (collectively, the
"Tenant Letters") in substantially the form attached hereto as Exhibit F-1,
informing them of the change in ownership of the respective Properties, and a
letter, duly executed by Seller, to each of the other parties to the Oakton
Contracts and the Towngate Contracts being assumed by Purchaser (collectively,
the "Contractor Letters"), in substantially the form attached hereto as Exhibit
F-2, informing them of the change in ownership of the respective Properties;

                    (13) an amount, paid in immediately available federal funds
to the Settlement Agent, equal to and in payment of all amounts payable by
Seller under Section 11(a) hereof;

                    (14) Foreign Investment in Real Property Tax Act Affidavit,
duly completed by Seller, substantially in the form of Exhibit G attached
hereto;

                    (15) copies of certificates of good standing of Seller
certified by an appropriate official of the State of Delaware and of the
Commonwealth of Virginia, respectively, and dated as of a date not earlier than
thirty (30) days before the Closing Date; a partnership resolution; a resolution
from the general partner of Seller; and an incumbency certificate to evidence
Seller's capacity and authority to consummate the Closing;

                    (16) certificate that the representations and warranties of
Seller specified in Section 7 hereof are true and accurate in all material
respects as of the Closing Date;

                    (17) an owner's title affidavit with respect to each of the
Oakton Property and the Towngate Property, in substantially the form attached
hereto as Exhibit H;

                    (18) to the extent in Seller's possession or under the
reasonable control of the Seller, and not previously delivered to Purchaser,
originals (or copies, if originals are not available) of all documents and books
and records reasonably related to and necessary for the continued operation of
each of the Properties, including without limitation lease files, rent records,
escalation records, and maintenance records (but specifically excluding any
confidential business records of Seller); and

                    (19) such other instruments, agreements, and documents as
may be reasonably required to consummate the transactions contemplated hereby,
provided the same do not increase Seller's obligations or liabilities beyond
those otherwise created by this Agreement, including without limitation a
settlement statement specifying the charges, credits, and adjustments to each
party to the transaction.

               (ii) Subject to any actions taken by Seller between the Effective
Date and the Closing Date in accordance with the provisions of this Agreement,
the representations and warranties of Seller contained in this Agreement as of
the Effective Date shall be true and correct in all material respects at and as
of the Closing Date, as if such representations and warranties were made at and
as of the Closing Date, and Seller shall have performed and

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<PAGE>

complied with all covenants, agreements, conditions, terms, and provisions of
this Agreement required to be performed or complied with by Seller prior to or
at the Closing.

               (iii) Title to each of the Properties shall conform with the
requirements of Section 4.

               (iv) Seller shall use commercially reasonable efforts, which
shall not include any expenditure of funds, to deliver to Purchaser, not later
than 5:00 o'clock p.m. (Virginia local time) on or before November 21, 2005, (1)
an executed and dated estoppel certificate from the owners association of the
Towngate Property in substantially the form attached hereto as Exhibit I-1, and
(2) an executed and dated estoppel certificate in substantially the form
attached hereto as Exhibit I-2 from the Oakton Tenants and the Towngate Tenants
and from any subtenant of either the Oakton Tenants or the Towngate Tenants (a
"Subtenant"); provided, however, that, with respect to each Subtenant, the form
of Exhibit I shall be appropriately modified to reflect that it is in connection
with a sublease), and provided further, however, (A) that Seller shall not have
any liability if and in the event any one or more of such estoppel certificates
is not received by Purchaser; and (B) that in the event that Purchaser does not
terminate this Agreement on or before the Study Period Termination Date pursuant
to and in accordance with Section 12 hereof, then, unless Seller and Purchaser
otherwise have agreed in writing, Purchaser shall be deemed to have approved the
form and substance of all such estoppel certificates delivered by Seller on or
before the Study Period Termination Date and to have waived the requirement of
the receipt of an estoppel certificate from any Oakton Tenant or any Towngate
Tenant or any Subtenant which has not been delivered by Seller on or before the
Study Period Termination Date. In connection with the foregoing, Seller and
Purchaser each confirms and agrees that Seller shall have satisfied its
obligations hereunder by delivering to Purchaser on or before November 21, 2005,
executed and dated estoppel certificate from those Oakton Tenants who
collectively lease at least 80% of the Oakton Property and from those Towngate
Tenants who collectively lease at least 80% of the Towngate Property.

          (B) SELLER'S CONDITIONS. Seller's obligation to deliver title to each
of the Properties and to otherwise consummate the transactions contemplated
hereby shall be subject to compliance by Purchaser with the following conditions
precedent on and as of the Closing Date:

               (i) Purchaser shall deliver to Seller (or to the Settlement Agent
acting on Seller's behalf) the Purchase Price Balance (subject to adjustments
and prorations), and any such instruction, as may be necessary, to release the
Deposit and apply it to payment of the Purchase Price.

               (ii) Purchaser shall deliver to Seller (or to the Settlement
Agent acting on Seller's behalf) on or before the Closing Date the following
("Purchaser's Closing Documents"):

                    (1) duly executed and acknowledged counterparts of the
Oakton Lease Assignment, the Towngate Lease Assignment, the Oakton General
Assignment, the Towngate General Assignment, the Tenant Letters, and the
Contractor Letters;

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<PAGE>

                    (2) an amount, payable in immediately available funds to the
Settlement Agent, equal to and in payment of all amounts payable by Purchaser
under Section 11(a) hereof;

                    (3) a copy of the certificate of good standing of Purchaser
certified by an appropriate official of the State of Purchaser's organization
and a copy of a current good standing certificate of Purchaser from the
Commonwealth of Virginia, each dated as of a date not earlier than thirty (30)
days before the Closing Date; and such resolutions and incumbency certificates
as are reasonably necessary to evidence Purchaser's capacity and authority to
consummate the Closing;

                    (4) a certificate that the representations and warranties of
Purchaser specified in Section 8 hereof are true and correct in all material
respects as of the Closing Date; and

                    (5) such other instruments, agreements, and documents as may
be reasonably required to consummate the transactions contemplated hereby,
provided that the same do not increase Purchaser's obligations or liabilities
beyond those otherwise created by this Agreement, including without limitation a
settlement statement specifying the charges, credits, and adjustments to each
party.

               (iii) Subject to any actions taken by Purchaser between the
Effective Date and the Closing Date in accordance with the provisions of this
Agreement, the representations and warranties of Purchaser contained in this
Agreement as of the Effective Date shall be true and correct in all material
respects at and as of the Closing Date as if such representations and warranties
were made at and as of the Closing Date, and Purchaser shall have performed and
complied with all covenants, agreements, conditions, terms, and provisions of
this Agreement required to be performed or complied with by Purchaser prior to
or at the Closing.

          (C) CONDITIONS GENERALLY. The foregoing conditions are for the benefit
only of the party for whom they are specified to be conditions precedent, and
such party may, in its sole discretion, waive any or all of such conditions and
proceed to Closing under this Agreement without any increase in, abatement of,
or credit against the Purchase Price except as expressly provided herein.

          (D) CLOSING DELIVERY COVENANTS.

               (i) Seller agrees that, provided that Purchaser is not in default
hereunder and Seller is otherwise required to close hereunder, Seller shall
deliver to Purchaser (or to the Settlement Agent) Seller's Closing Documents on
or before the Closing Date.

               (ii) Purchaser agrees that, provided Seller is not in default
hereunder and Purchaser is otherwise obligated to close hereunder, Purchaser
shall deliver to Seller (or to the Settlement Agent on Seller's behalf) the
Purchase Price Balance (as adjusted) and Purchaser's Closing Documents on or
before the Closing Date.

                                       10

<PAGE>

     7. SELLER'S REPRESENTATIONS.

          (A) REPRESENTATIONS. Seller represents and warrants to Purchaser as of
the Effective Date and as of the Closing as follows:

               (i) GOOD STANDING. Seller is a limited partnership that has been
duly organized and is validly existing under the laws of the State of Delaware,
and is in good standing under the laws of the Commonwealth of Virginia.

               (ii) AUTHORITY. Seller has full power, right, and authority to
enter into and perform its obligations under this Agreement and the other
agreements contemplated herein to be executed and performed by it, and has taken
all necessary action to authorize the execution, delivery, and performance of
this Agreement.

               (iii) DEFAULTS. The execution and delivery of this Agreement and
the other agreements contemplated herein, and the consummation of the
transactions contemplated hereby on the part of Seller, to the actual knowledge
of Seller, do not and will not (1) except as to the transfer of any of the
Oakton Permits or the Towngate Permits, require any governmental or other
consent; (2) violate or conflict with any judgment, injunction, award, decree,
or order of any court applicable to or affecting Seller or either of the
Properties; (3) violate or conflict with any law or governmental regulation
applicable to Seller or either of the Properties; (4) violate or conflict with
any provision of any agreement or instrument to which Seller is a party or which
relates to or affects either of the Properties; or (5) violate, conflict with,
or result in the breach or termination of, or constitute a default under, the
organizational documents of Seller.

               (iv) BINDING OBLIGATION. Upon the assumption that this Agreement
constitutes the legal, valid, and binding obligation of Purchaser, this
Agreement constitutes the legal, valid, and binding obligation of Seller
enforceable in accordance with its terms, subject to bankruptcy, insolvency,
reorganization, moratorium, or similar laws affecting the enforceability of
creditors' rights generally.

               (v) NON-FOREIGN PERSON. Seller is a "non-foreign person" within
the meaning of Section 1445 of the Internal Revenue Code of 1986, as amended,
and the regulations issued thereunder (the "Code").

               (vi) BANKRUPTCY. Neither Seller nor any of Seller's property is
in the hands of a receiver nor is any application for a receiver or dissolution
pending; Seller has not made an assignment for the benefit of creditors; Seller
has not filed, and to its actual knowledge there has not been filed against it,
any petition in bankruptcy; and to the best knowledge of Seller, none of the
foregoing is pending or threatened.

               (vii) LITIGATION. There is not pending any action, suit, or
proceeding against Seller or either of the Properties, and, to the actual
knowledge of Seller, no such action, suit, or proceeding is threatened against
Seller or either of the Properties, and Seller has not received any written
notice threatening any action, suit, or proceeding against Seller or either of
the Properties.

                                       11

<PAGE>

               (viii) LEASES.

                    (1) The leases with respect to the Oakton Property are
specified on Exhibit J-1 (collectively, the "Oakton Leases"); (2) the copies of
the Oakton Leases provided or to be provided to Purchaser by Seller are true,
accurate, and complete, and each of the Oakton Leases is in full force and
effect; (3) neither any tenant under a Oakton Lease (each, a "Oakton Tenant")
nor Seller is in default under any Oakton Lease, and, to Seller's actual
knowledge, there does not exist any condition, which, with the passage of time
or the giving of notice, shall constitute a default under any Oakton Lease, or
any unsatisfied claim, set-off, or counterclaim against Seller by any Oakton
Tenant; (4) there is not any action or proceeding pending, or, to Seller's
actual knowledge, threatened, by any Oakton Tenant against Seller; (5) each of
the Oakton Leases represents the complete agreement between Seller and the
respective Oakton Tenant as to all rights, liabilities, and obligations of
Seller and said Oakton Tenant in and to the property demised thereunder, and
none of the Oakton Leases has been modified or amended except as set forth in
Exhibit J-1; (6) the security deposits set forth on Exhibit K with respect to
the Oakton Tenants are all of the security deposits paid by or on behalf of
Oakton Tenants under the Oakton Leases; (7) no Oakton Tenant has paid any rent
or other charge of any nature for a period of more than one month in advance;
and (8) the rent roll with respect to the Oakton Property attached hereto as
Exhibit L-1 is true and correct in all material respects as of the Effective
Date. There also are specified on Exhibit J-1, to the best knowledge,
information and belief of Seller, those certain subleases with respect to the
Oakton Property.

                    (2) The leases with respect to the Towngate Property are
specified on Exhibit J-2 (collectively, the "Towngate Leases"); (2) the copies
of the Towngate Leases provided or to be provided to Purchaser by Seller are
true, accurate, and complete, and each of the Towngate Leases is in full force
and effect; (3) neither any tenant under a Towngate Lease (the "Towngate
Tenant") nor Seller is in default under any Towngate Lease, and, to Seller's
actual knowledge, there does not exist any condition, which, with the passage of
time or the giving of notice, shall constitute a default under any Towngate
Lease, or any unsatisfied claim, set-off, or counterclaim against Seller by any
Towngate Tenant; (4) there is not any action or proceeding pending, or, to
Seller's actual knowledge, threatened, by any Towngate Tenant against Seller;
(5) each of the Towngate Leases represents the complete agreement between Seller
and the respective Towngate Tenant as to all rights, liabilities, and
obligations of Seller and said Towngate Tenant in and to the property demised
thereunder, and none of the Towngate Leases has been modified or amended except
as set forth in Exhibit J-2; (6) the security deposits set forth on Exhibit K
with respect to the Towngate Tenants are all of the security deposits paid by or
on behalf of Towngate Tenants under the Towngate Leases; (7) no Towngate Tenant
has paid any rent or other charge of any nature for a period of more than one
month in advance; and (8) the rent roll with respect to the Towngate Property
attached hereto as Exhibit L-2 is true and correct in all material respects as
of the Effective Date. There also are specified on Exhibit J-2, to the best
knowledge, information and belief of Seller, those certain subleases and access
agreements with respect to the Towngate Property.

               (ix) BROKERAGE AGREEMENTS. All leasing brokerage contracts and
amendments and modifications thereto affecting the Oakton Property (the "Oakton
Leasing Brokerage Contracts") are specified on Exhibit M-1, and all leasing
brokerage contracts and

                                       12

<PAGE>

amendments and modifications thereto affecting the Towngate Property (the
"Towngate Leasing Brokerage Contracts") are specified on Exhibit M-2. All sums
due and payable under the Oakton Leasing Brokerage Contracts and the Towngate
Leasing Brokerage Contracts have been paid by Seller except for that certain
second installment of commission in the amount of $16,203.15 (the "World Hope
Commission") due on January 1, 2007, with respect to the lease for World Hope
International as specified on Exhibit M-2. Seller and Purchaser each confirms
and agrees that Purchaser shall assume sole liability for the payment of the
World Hope Commission, as and when due and payable, and shall indemnify, defend,
and hold harmless Seller with respect to said payment of the World Hope
Commission, and shall receive at Closing a credit from Seller in the amount of
$16,203.15 in consideration therefor. This provision shall survive the Closing
and shall remain in full force and effect until the payment in full by Purchaser
of the World Hope Commission.

               (x) CONTRACTS. Third party vendor contracts for the Oakton
Property are specified on Exhibit N-1 (collectively, the "Oakton Contracts"),
and third party vendor contracts and a cost sharing agreement for the Towngate
Property are specified on Exhibit N-2 (collectively, the "Towngate Contracts").
Seller shall deliver to Purchaser true and complete copies of each of the Oakton
Contracts and the Towngate Contracts, including all amendments and modifications
thereto. Each of the Oakton Contracts and the Towngate Contracts presently is in
full force and effect, and Seller is not in default under any of the Oakton
Contracts or the Towngate Contracts, and, to the actual knowledge of Seller, no
other party thereto is in default.

               (xi) PERMITS. There are listed in Exhibit O-1 all Permits
actually held by Seller in connection with its ownership of the Oakton Property
(the "Oakton Permits") and in Exhibit O-2 all Permits actually held by Seller in
connection with its ownership of the Towngate Property (the "Towngate Permits").
To its actual knowledge, Seller has not received any written notice from any
governmental authority claiming that Seller or either of the Properties does not
possess any license or permit required in connection with the ownership or
operation of the Properties, which notice has not been entirely complied with.

               (xii) ENVIRONMENTAL.

                    (1) Without additional inquiry or investigation, and except
as may be disclosed in (1) that certain Phase I Environmental Site Assessment of
Apex Environmental, Inc. dated April 23, 1999, (2) that certain Phase I
Environmental Site Assessment Update of ATC Associates, Inc. dated March 24,
2000, and (3) that certain Remediation of Mold Impacted Building Materials -
Final Report of HP Environmental, Inc. dated September 20, 2003 (the "HP
Environmental Report"), Seller does not have any actual knowledge of the
presence of any "Hazardous Substance" (as hereinafter defined) on, under or at
either of the Properties. Seller has not received any written notice from any
federal, state, county, municipal, or other governmental department, agency, or
authority concerning any Hazardous Substance on either of the Properties. To the
actual knowledge of Seller, none of its agents or employees has used, generated,
stored, transported, manufactured, treated, released, or disposed of any
Hazardous Substance, in, under, or about either of the Properties in violation
of any "Environmental Law" (as hereinafter defined). Except for that certain
underground oil storage tank located on the Oakton Property, there is not
presently, to Seller's actual knowledge,

                                       13

<PAGE>

any storage tank on or under either of the Properties. Other than as disclosed
in the HP Environmental Report, Seller to its actual knowledge has not received
any notice of the presence of elevated concentrations of fungal propagules in
the Properties.

                    (2) "Hazardous Substance" shall mean petroleum, PCB's,
radioactive materials, asbestos, or any materials containing asbestos, or any
other "hazardous substance" or "toxic substance" as either of those two terms
are defined in the Comprehensive Environmental Response, Compensation and
Liability Act of 1980, as amended by the Superfund Amendments and
Reauthorization Act (42 U.S.C. Sections 9601 et seq.), or the Resource
Conservation and Recovery Act (42 U.S.C. Sections 6901 et seq.), and the
regulations adopted pursuant thereto, or in any environmental law or regulation
of the Commonwealth of Virginia or of any political subdivision thereof
affecting either of the Properties (collectively, the "Environmental Laws").
Hazardous Substances shall not be deemed to include any lead-based paint or
materials related thereto, and Seller makes no representation or warranty with
respect thereto.

                    (3) Notwithstanding the foregoing, the terms and conditions
of the preceding two subparagraphs shall not apply to the presence, use,
storage, manufacture, release, or disposal of Hazardous Substances that are
generally recognized to be appropriate to the normal and customary uses to which
either of the Properties is being put, or relate to the maintenance of either of
the Properties, and, in either case, are not in excess of any applicable legal
limits and are used and stored in compliance with all applicable Environmental
Laws.

               (xiii) CONDEMNATION. There is not pending, or to Seller's actual
knowledge threatened, any condemnation or eminent domain proceeding affecting
any portion of either of the Properties.

               (xiv) TAX PROCEEDINGS. A true, correct, and complete description
of any administrative and court proceeding currently pending, or which may be
instituted prior to the Closing Date, for refunds or adjustments of real estate
taxes and assessments levied, assessed, or pending against either of the
Properties or to reduce the assessed valuation of either of the Properties (any
of the foregoing, a "Tax Proceeding") is set forth in Exhibit P hereto.

               (xv) TENANT IMPROVEMENT ALLOWANCES. There are specified on
Exhibit Q those certain tenant improvement allowances (collectively, the "TI
Allowances") with respect to certain of the Oakton Tenants and the Towngate
Tenants under their respective Leases. Seller and Purchaser each confirms and
agrees that Purchaser shall assume sole liability for and with respect to the TI
Allowances, and shall indemnify, defend, and hold harmless Seller with respect
to the TI Allowances, and shall receive at Closing a credit from Seller in the
amount of $107,388.30 in consideration therefor. This provision shall survive
the Closing and shall remain in full force and effect until the payment in full
by Purchaser of all of the TI Allowances.

               (xvi) NO ZONING VIOLATION NOTICE. Seller has delivered to
Purchaser (1) that certain letter from the Fairfax County, Virginia Office of
Comprehensive Planning dated January 14, 1997 with respect to zoning matters
related to the Oakton Property, and (2) that certain letter from the City of
Alexandria, Virginia Department of Planning and Zoning dated

                                       14

<PAGE>

April 1, 1999 with respect to zoning matters related to the Towngate Property.
Seller, to its actual knowledge, has not received any notice:

                    (A) from any state, county or municipal authority alleging
any building or zoning violation of law in respect of either of the Properties,
including, without limitation, the occupancy or operation thereof; or

                    (B) concerning any change in the zoning classification of
either of the Properties.

               (xvii) OTHER LIABILITIES. Except as otherwise disclosed in or
provided for under this Agreement and the Exhibits and Schedules attached
hereto, and except for the ordinary operating costs and expenses associated with
the Properties, to Seller's actual knowledge, there are no current material
unfunded liabilities under any contract, easement agreement, or similar document
appurtenant to the Properties that would become a binding obligation of
Purchaser upon acquisition of the Properties.

          (B) LIMITATIONS ON SELLER'S REPRESENTATIONS AND WARRANTIES. The
expiration after the Effective Date of any Lease in accordance with its terms
(other than by reason of default by a party thereto) shall not be deemed to make
any representation or warranty of Seller untrue as of the Closing Date, nor
shall such expiration affect the obligation of Purchaser to close hereunder. So
long as Seller provides to Purchaser a then-current aging report of the status
of rental properties under the Oakton Leases and the Towngate Leases on November
21, 2005, the occurrence of any rent arrearage under the Leases after the
Effective Date shall not be deemed to make any representation or warranty of
Seller untrue as of the Closing Date, nor shall such change affect the
obligation of Purchaser to close hereunder.

          (C) NO OTHER REPRESENTATIONS OR WARRANTIES. Purchaser acknowledges
that (i) Purchaser has examined or will examine each of the Properties and is
familiar with the physical condition thereof and has conducted such
investigation of the affairs of each of the Properties as Purchaser has
considered appropriate; (ii) except to the extent specifically set forth herein
and in the Seller's Closing Documents, neither Seller nor any of the employees,
agents or attorneys of Seller has made any verbal or written representation,
warranty, promise, or guarantee whatsoever to Purchaser, whether express or
implied (including, without limitation, with respect to the physical condition
or operation of either of the Properties; the actual or projected revenue and
expenses of either of the Properties; the zoning and other laws, regulations and
rules applicable to either of the Properties or the compliance of either of the
Properties therewith; the quantity, quality, or condition of the articles of
personal property and fixtures included in the transaction contemplated hereby;
or the use or occupancy of either of the Properties or any part thereof),
affecting or related to either of the Properties or the transactions
contemplated hereby; (iii) Purchaser has not relied upon any statement made in
any informational brochure with respect to either of the Properties; and (iv)
except for the representations, warranties and covenants of Seller expressly set
forth herein and in the Seller's Closing Documents, Purchaser has entered into
this Agreement in reliance solely on its own independent investigation,
inspection, analysis, appraisal, examination, and evaluation of relevant facts
and circumstances.

                                       15

<PAGE>

          (D) SELLER'S KNOWLEDGE. As used in this Agreement or in any
representation, warranty, or certification made or provided by Seller in
accordance with this Agreement, the phrase "to the actual knowledge of Seller"
or words of similar import shall mean the knowledge of each of Scott W. Jenkins
in his capacity as the President of E. L. Vaduz Enterprises, Inc., the sole
general partner of Seller, and Theresa F. McLaughlin, in her capacity as
Secretary of ELV Associates, Inc. the property manager of each of the Properties
for Seller, with the obligation or duty to investigate and review the records
and files pertaining to each of the Properties, but without other investigation.

     8. PURCHASER'S REPRESENTATIONS.

          (A) REPRESENTATIONS. Purchaser represents and warrants to Seller as
follows:

               (i) GOOD STANDING. Purchaser has been duly organized and is
validly existing and in good standing under the laws of the State of its
organization, and is in good standing under the laws of the Commonwealth of
Virginia.

               (ii) AUTHORITY. Purchaser has full power, right, and authority to
enter into and perform its obligations under this Agreement and the other
agreements contemplated herein to be executed and performed by it, and has taken
all necessary action to authorize the execution, delivery, and performance of
this Agreement.

               (iii) BANKRUPTCY. Neither Purchaser nor any of Purchaser's
property is in the hands of a receiver nor is any application for a receiver or
dissolution pending; Purchaser has not made an assignment for the benefit of
creditors; Purchaser has not filed, and to its actual knowledge there has not
been filed against it, any petition in bankruptcy; and to the best knowledge of
Purchaser, none of the foregoing is pending or threatened.

               (iv) DEFAULT. The execution and delivery of this Agreement and
the other agreements contemplated herein, and the consummation of the
transactions contemplated hereby on the part of Purchaser, to the actual
knowledge of Purchaser, do not and will not (1) except as to the transfer of the
Oakton Permits or the Towngate Permits, require any governmental or other
consent; (2) violate or conflict with any judgment, injunction, award, decree or
order of any court applicable to or affecting Purchaser, or any provision of any
agreement or instrument to which Purchaser is a party; (3) violate or conflict
with any law or governmental regulation applicable to Purchaser; (4) violate or
conflict with any provision of any agreement or instrument to which Purchaser is
a party; or (5) violate, conflict with, or result in the breach or termination
of, or constitute a default under, the organizational documents of Purchaser.

               (v) BINDING OBLIGATION. Upon the assumption that this Agreement
constitutes the legal, valid, and binding obligation of Seller, this Agreement
constitutes the legal, valid, and binding obligation of Purchaser enforceable in
accordance with its terms, subject to bankruptcy, insolvency, reorganization,
moratorium, or similar laws affecting the enforceability of creditors' rights
generally.

                                       16

<PAGE>

               (vi) LITIGATION. There is not pending any action, suit, or
proceeding against Purchaser, and, to the actual knowledge of Purchaser, no such
action, suit, or proceeding is threatened against Purchaser, which might have a
material adverse effect on the ability of Purchaser to perform its obligations
under this Agreement.

          (B) PURCHASER'S KNOWLEDGE. As used in this Agreement or in any
representation, warranty, or certification made or provided by Purchaser in
accordance with this Agreement, the phrase "to the actual knowledge of
Purchaser" or words of similar import shall mean the knowledge of each of Oliver
T. Carr, III, Chief Executive Officer of Purchaser, and Clint Fisch, Director of
Acquisitions of Purchaser, in his capacity as Purchaser's representative with
the obligation or duty to investigate and review the records and files
pertaining to the Purchaser, but without other investigation.

     9. COVENANTS.

          (A) COVENANTS OF SELLER.

               (I) OPERATION AND MAINTENANCE OF PROPERTY. During the period
between the Effective Date and the Closing Date, Seller shall operate each of
the Oakton Property and the Towngate Property in the normal course of business,
in a manner consistent in all material respects with the respective management
and operation of the Oakton Property and the Towngate Property prior to the
Effective Date.

               (II) LEASES. Seller, during the period between the Effective Date
and the Closing Date, (1) shall not enter into, modify, amend, or terminate any
Oakton Lease or Towngate Lease without Purchaser's prior written consent, which
consent shall not be unreasonably withheld, conditioned, or delayed, and (2)
shall not consent to any subleasing, assignment, or tenant alteration under any
Oakton Lease or Towngate Lease, without Purchaser's prior written consent, which
consent shall not be unreasonably withheld, conditioned, or delayed. Seller
shall deliver to Purchaser a notice of each proposed action hereunder, stating,
if applicable, whether Seller is willing to consent to such action and setting
forth the relevant information therefor, and, if applicable, the number of days
within which Seller must respond to the proposed action under the terms of the
applicable Oakton Lease or Towngate Lease, and any other material information
supplied to Seller as to the proposed action or reasonably necessary for
Purchaser to make a determination as to the proposed action. Purchaser shall
have five (5) business days after delivery to it of such notice and information
to determine whether or not to approve such action. If any Lease requires that
Seller's consent be given in the circumstances, then Purchaser shall be deemed
ipso facto to have approved such action. If any Oakton Lease or Towngate Lease
requires that Seller's consent not be unreasonably withheld, conditioned, or
delayed in the circumstances, then Purchaser's consent shall not be unreasonably
withheld, conditioned, or delayed.

               (III) CONTRACTS. Seller during the period between the Effective
Date and the Closing Date, shall not, without Purchaser's prior written consent,
which shall not be unreasonably withheld, conditioned or delayed, enter into any
new service, maintenance, or

                                       17

<PAGE>

operating agreement unless the same is reasonably necessary for the normal
operation of either of the Properties prior to the Closing Date.

          (B) COVENANTS OF PURCHASER. Purchaser acknowledges that all
information in respect of the Properties furnished to Purchaser is and has been
so furnished on the condition that Purchaser maintain the confidentiality
thereof. Accordingly, Purchaser shall, and shall inform its partners, directors,
officers, employees, agents, contractors, and representatives to, hold in strict
confidence, and not disclose to any other person or entity without the prior
written consent of Seller until the Closing shall have been consummated, any of
the information in respect of either of the Properties delivered to Purchaser by
Seller or any of its agents, representatives, directors, officers, or employees
(the "Confidential Information"). If the Closing does not occur and this
Agreement is terminated, Purchaser shall use commercially reasonable efforts to
promptly return, or cause to be returned, to Seller all copies of such
Confidential Information without retaining, or knowingly permitting retention
of, any copy thereof. Notwithstanding anything to the contrary hereinabove set
forth, Purchaser may disclose such Confidential Information (i) on a
need-to-know basis to its employees, its title insurer, and members of
professional firms serving it in connection with this transaction, including
without limitation its attorneys, architects, environmental consultants and
engineers, and its prospective assignees and lenders; (ii) as any governmental
agency or authority may require in order to comply with applicable laws or
regulations; and (iii) if required by an order of any court of competent
jurisdiction, and this provision shall survive Closing. Confidential Information
does not include any information which (1) at the time of disclosure is
generally available to and known by the public; (2) was available on a
non-confidential basis; and (3) has been independently developed by Purchaser.
Purchaser also agrees that following Closing it shall provide Seller, upon
reasonable advance notice and during normal business hours, access to those
documents related to either the Oakton Property or the Towngate Property
provided by Seller to Purchaser pursuant to this Agreement for purposes of
inspection and copying at Seller's sole cost and expense.

     10. APPORTIONMENTS. The terms and provisions of this Section 10 shall apply
to each of the Oakton Property and the Towngate Property:

          (A) To the extent practicable, all items of income and expense,
including the following items, shall be apportioned between Seller and Purchaser
on the Closing Date. In the event final figures have not been reached on any of
the adjustments or prorations which are to be made at or prior to Closing
pursuant to this Section 10, the parties shall close using adjustments and
prorations reasonably estimated by Seller and Purchaser, subject to later
readjustment when such final figures have been obtained. If more current
information is not available, estimates shall be based upon the prior operating
history of the Oakton Property or Towngate Property, as may be applicable, as
shown on the most recent management reports available, annualizing operating
income and expenses where appropriate. The parties hereto agree that they shall
seek to determine the amounts of all prorations and adjustments required
hereunder on or before the Closing Date, if possible, and to the extent not then
obtainable, as soon as practicable thereafter, but in any event not later than
May 31, 2006. If by May 31, 2006, Seller and Purchaser are unable to agree upon
any one or more of the required prorations or adjustments, Seller and Purchaser
shall appoint an independent accounting firm which shall review the disputed

                                       18

<PAGE>

prorations or adjustments within thirty (30) days after such appointment. Seller
and Purchaser agree to cooperate with said independent accounting firm and
provide it with such information as it reasonably requests to enable it to make
such determination. The determination by the independent accounting firm with
respect to the correctness of each item in dispute shall be conclusive and
binding on Seller and Purchaser. All fees and expenses billed by the independent
accounting firm in connection with the resolution of disputes under this Section
10 shall be borne one-half (1/2) by the Seller and one-half (1/2) by the
Purchaser. All adjustments as determined hereunder shall be paid to Seller or
Purchaser, as the case may be, in cash or immediately available funds within
five (5) business days after written notice of such final adjustment amount has
been delivered to the appropriate obligated party (Seller or Purchaser, as the
case may be).

               (i) All base rents collected by Seller through the Closing Date
(1) which are allocable to the period through the Closing Date shall be retained
by Seller as the property of Seller, and (2) which are allocable to the period
commencing on the day immediately following the Closing Date shall be paid by
Seller to Purchaser on the Closing Date as a credit against the Purchase Price.
All base rents that have accrued to and remain unpaid through the Closing Date
shall belong to Seller, and shall be remitted to Seller as and when collected by
Purchaser in the manner specified in the immediately succeeding sentence (and
with respect to amounts payable to Seller, Purchaser shall not have any
obligation to collect such amounts). All base rents collected by Purchaser after
the Closing Date shall be applied, first, to current rent due, then to reimburse
Purchaser for its costs and expenses of collection, and then to reimburse Seller
for past rent due starting with the most recent delinquency. For the purposes of
this subparagraph, all base rents shall be apportioned on a daily basis using
the number of days in the month in which the Closing Date occurs. Seller, at
Seller's expense and after notice to Purchaser, shall be entitled to institute
collection actions against any tenant for the recovery of any delinquent base
rent due to Seller, and Purchaser agrees to cooperate reasonably with Seller (at
no cost, expense, or liability to Purchaser) in the prosecution of any such
collection efforts; provided, however, Seller shall have no right to commence or
maintain any lawsuit or other legal proceeding against any tenant of the
Properties with respect to delinquent rent after the Closing.

               (ii) All monthly or other payments made by tenants in advance
based upon (1) projected or estimated additional rent, (2) increases in
operating expenses of the Oakton Property or Towngate Property, as may be
applicable, over base operating expenses, (3) increases in real estate taxes
with respect to the Oakton Property or the Towngate Property, as may be
applicable, over base real estate taxes, or (4) any other similar matter (the
"Additional Rent") shall be prorated between Seller and Purchaser as of the
Closing Date based upon the actual number of days in the monthly or other period
for which the advance payment is made. In connection with the foregoing and with
the provisions of subsection (a) hereof, Seller and Purchaser each acknowledges
and agrees that a reconciliation of the aggregate Additional Rent received for
the calendar year 2005 as compared with the total operating expenses and real
estate taxes paid by either Seller and Purchaser for the calendar year 2005 may
be necessary following the Closing to take into account any excess or deficiency
in the amount of operating expenses or real estate taxes paid by either party
over the aggregate Additional Rent received by said party from tenants of the
Properties during the 2005 calendar year. The parties agree to cooperate
reasonably in arriving at any such necessary reconciliation and to make
available to each other

                                       19

<PAGE>

such information from records in their possession as may be necessary in
connection with such reconciliation.

               (iii) All taxes, general and special, and all other public or
governmental charges or assessments against the Oakton Property or the Towngate
Property, as may be applicable, for the current tax year of the Property, which
are or may be payable on an annual basis (including Metropolitan District,
Sanitary Commission, or other benefit charges, assessments, liens, or
encumbrances for sewer, water, drainage or other public improvements completed
or commenced on or prior to the Effective Date, or subsequent thereto) shall be
apportioned between the parties on the Closing Date, and paid thereafter by the
Purchaser except for any such taxes previously paid for by Seller for which
Seller has received a credit hereunder.

               (iv) All water rates and charges, unless the same are the direct
responsibility of any Tenant (and provided that any such charges are then being
paid by such Tenant(s)).

               (v) Sewer and vault taxes and rents.

               (vi) All charges and payments for fuel and steam, gas,
electricity, and all other utility services supplied to the Oakton Property or
the Towngate Property, as may be applicable, which are not charged directly to
Tenants; provided, however, that if there is no meter or if the current bill for
any of such utilities has not been issued prior to the Closing Date, the parties
agree that the charges therefor shall be adjusted at the Closing on the basis of
the charges for the prior period for which bills were issued.

               (vii) All amounts paid or payable under the Contracts being
assumed by Purchaser, if any, shall be adjusted and apportioned as of the
Closing Date.

               (viii) Any and all security deposits and prepaid rent, and all
interest earned thereon shall be a credit to Purchaser at Closing. Seller shall
assign to Purchaser, and shall receive credit (on a dollar-for-dollar basis)
for, the deposits, if any, made by Seller in connection with the provision of
electric, sewer, water, telephone, and other utility services to the Oakton
Property or the Towngate Property, as may be applicable.

               (ix) For purposes of calculating prorations, Seller shall be
deemed entitled to the income from the Oakton Property or the Towngate Property,
as may be applicable, and responsible for the expenses thereof for the entire
day upon which the Closing occurs. All such prorations shall be made on the
basis of the actual number of days of the month which shall have elapsed as of
the day of the Closing and based upon the actual number of days in the month and
a three hundred sixty-five (365) day year.

          (B) Seller shall endeavor to furnish readings of the water, gas and
electric meters, if any, located on the Oakton Property or the Towngate
Property, as may be applicable, other than meters measuring the computation of
utilities which are the direct responsibility of any Tenant, to a date not more
than five (5) days prior to the Closing Date, and the unfixed water rates and
charges, sewer taxes and rents, and gas and electricity charges, if any, based
thereon for the intervening time shall be apportioned on the basis of such last
readings. If such readings are

                                       20
<PAGE>

not obtainable by the Closing Date, then, at Closing, any water rates and
charges, sewer taxes and rents, and gas and electricity charges which are based
on such readings shall be prorated based upon the per diem charges obtained by
using the most recent period for which such readings shall then be available.
Upon the taking of subsequent actual readings, such items shall be apportioned
after the Closing Date.

          (C) The amount of any unpaid real property taxes and assessments,
water rates and charges, and sewer taxes and rents which Seller is obligated to
pay and discharge may, at the option of Seller, be credited to the Purchase
Price Balance, provided that official bills therefor, indicating the interest
and penalties, if any, thereon up to and including the Closing Date, are
furnished by Seller to Purchaser at the Closing.

          (D) Subject to subsection (f) hereof, if any refunds of real property
taxes or assessments, water rates and charges, or sewer taxes and rents shall be
made after the Closing, the same shall be held in trust by Seller or Purchaser,
as the case may be, and shall first be applied to the unreimbursed costs
incurred in obtaining the same, then paid to any tenant who is entitled to the
same, and the balance, if any, shall be paid to Seller (for the period through
the Closing Date) and to Purchaser (for the period commencing on the day
immediately following the Closing Date).

          (E) In the event the apportionments hereinabove provided which are
made at the Closing result in a credit balance to either party, such sum shall
be adjusted at Closing by an increase or reduction, as the case may be, of the
Purchase Price Balance payable at Closing.

          (F) If any of the Tax Proceedings shall be continuing as of the
Closing Date, Seller shall, from and after the Closing Date, be entitled to
control the prosecution of said Tax Proceeding(s) to completion, and to settle
or compromise any claim therein, and, subject to the rights of tenants, Seller
shall be solely entitled to any proceeds (but not future savings) resulting from
the settlement or compromise of, or determination of, said Tax Proceeding(s),
and shall be liable solely for the costs related thereto. Purchaser agrees to
cooperate with Seller, at Seller's expense, and to execute any and all documents
reasonably required by Seller in furtherance of the foregoing.

     11. CLOSING MATTERS. The following items shall be provided for at the
Closing:

          (A) PAYMENT OF RECORDING, TITLE, AND OTHER FEES.

               (i) Seller and Purchaser shall each pay one half (1/2) of any and
all deed recordation and grantor taxes that may be imposed with respect to the
recordation of the Oakton Deed and the Towngate Deed. Purchaser shall be solely
responsible for the payment of any and all recordation taxes that may be imposed
with respect to the recordation of any deed of trust related to this
transaction.

               (ii) Purchaser shall pay all premiums, charges, and fees of the
Title Company in connection with the title examination and Title Policy, if any,
to be obtained by Purchaser; any recording costs and charges; any and all
recordation taxes in connection with

                                       21

<PAGE>

Purchaser's financing; and all charges and fees of the Settlement Agent other
than those paid by Seller in accordance with subparagraph (iii) hereof.
Purchaser shall pay all charges and fees of the surveyor in connection with any
survey of either of the Properties obtained by Purchaser. Purchaser shall pay
all tax certificate fees.

               (iii) Seller shall pay any reasonable fees charged Seller for
services rendered to it by the Settlement Agent.

               (iv) Other charges, if any, shall be paid in the manner in which
purchasers and sellers of real property in the Commonwealth of Virginia
customarily divide such charges; provided, however, that Seller and Purchaser
each shall be responsible for its own professional fees and expenses.

          (B) TRANSFER OF UTILITIES. As of Closing, the Purchaser shall be
responsible for the transfer of accounts and establishment of all utility
services to each of the Properties in the name of Purchaser. Seller shall
cooperate reasonably with Purchaser in this regard.

     12. STUDY PERIOD.

          (A) LENGTH OF STUDY PERIOD. During that period (the "Study Period")
commencing as of the Effective Date, and ending at 5:00 o'clock p.m. (Virginia
local time) on November 25, 2005 (the "Study Period Termination Date"),
Purchaser, and its employees, consultants, engineers, agents, and
representatives, at Purchaser's sole cost and expense, shall have the right,
subject to subsection (c) hereof, to conduct such feasibility studies of each of
the Properties, including without limitation architectural, engineering,
environmental, hydrologic, zoning, and development and economic feasibility
studies and investigations; audits of the books and records of Seller reasonably
related to each of the Properties; and conferences with governmental staff
members and the Oakton Tenants and the Towngate Tenants (collectively, the
"Feasibility Studies") as Purchaser deems necessary; provided, however, that
Purchaser shall not be permitted to undertake any soil borings or other
drillings on either of the Properties without prior written notice to, and
consent of, Seller. Seller shall cooperate reasonably with Purchaser and its
agents in permitting Purchaser and its agents full access to each of the
Properties, and all books, records, files, financial data relating to each of
the Properties, and the Oakton Leases and the Towngate Leases, and the Oakton
Contracts and the Towngate Contracts, to conduct the Feasibility Studies. Such
access shall be during normal business hours, after the giving of reasonable
advance notice to Seller, and subject to the rights of tenants. Purchaser, and
its employees, consultants, engineers, agents, and representatives, shall use
reasonable and diligent efforts to minimize interference with the management,
operation, use, or maintenance of any portion of either of the Properties by
Seller and its tenants, agents, contractors, and employees. The parties
acknowledge that Purchaser may be required to perform a historical audit of the
Properties in order to comply with Item 3-14 of Regulation S-X promulgated under
the Securities Act of 1933 and the Securities Exchange Act of 1934. Seller
shall, during the time period for which access is allowed hereunder, take
commercially reasonable efforts to permit Purchaser's auditors access at that
location where Seller customarily maintains its records, upon reasonable advance
notice and during normal business hours, to all of the Properties' books and
records and the operating statements (certified by an officer of the general
partner of Seller) and

                                       22

<PAGE>

property management balance sheets for the Properties for three (3) calendar
years prior to the Closing Date. To the extent that the originals or copies of
same are not otherwise provided by Seller to Purchaser at Closing, and to the
extent that the same are ordinarily maintained by Seller in its normal course of
business, such books and records shall include the detail general ledger of
profits and loss, accounts receivable records, and rent rolls. Buyer's access
rights shall commence on the Effective Date and shall continue until the earlier
to occur of (i) the termination of this Agreement by either Seller or Purchaser
in accordance with the terms of this Agreement or (ii) the successful completion
of the audit and the filing of the 3-14 report with the SEC, written notice of
which shall be delivered promptly by Purchaser to Seller. The foregoing
obligation shall fully survive the Closing. Notwithstanding anything to the
contrary in the foregoing, other than providing the access to Purchaser
specified herein, Seller shall not have any liability or responsibility in
connection with or in any manner related to, directly or indirectly, any audit
required to be made by Purchaser or any compliance required of Purchaser with
any Regulation under the Securities Act of 1933 or the Securities Act of 1934.

          (B) PURCHASER'S TERMINATION. Purchaser shall have the right, for any
reason or no reason at all, to terminate this Agreement by delivering to Seller
written notice of such termination at or before 5 o'clock p.m. (Virginia local
time) on the Study Period Termination Date. If Purchaser terminates this
Agreement in the manner set forth above, then the Deposit and all accrued
interest thereon shall be refunded to Purchaser, and no party shall have any
further rights, liabilities, or obligations in connection with this Agreement,
except for those which may arise under subsection (c) hereof. If Purchaser does
not terminate this Agreement in the manner set forth above, then this Agreement
shall remain and continue in full force and effect.

          (C) DUE DILIGENCE INDEMNITY. Purchaser agrees (i) to indemnify, defend
and hold harmless Seller, and its partners, agents, servants, and employees,
from and against any and all loss, cost, claim, or liability asserted against
Seller, or its partners, agents, servants, or employees, and expenses (including
without limitation reasonable attorneys' fees and disbursements incurred by
Seller in defending the same), in connection with any damage to either of the
Properties (including without limitation the costs of restoring either of the
Properties to its condition existing immediately prior to Purchaser's action, if
Purchaser fails to restore), or death or injury to any person which occurs as a
result of any act or omission of Purchaser or any of its employees, consultants,
engineers, agents, and representatives, during any entry onto or inspection of
either of the Properties, or during the conduct of any of the Feasibility
Studies on either of the Properties, by Purchaser or any of its employees,
consultants, engineers, agents, or representatives; and (ii) to restore each of
the Properties to its condition existing immediately prior to Purchaser's
action, if Purchaser terminates this Agreement in accordance with this Section
12. Purchaser will maintain, or cause to be maintained, in full force and
effect, at all times during which Purchaser, or its employees, consultants,
engineers, agents, or representatives, are on either of the Properties, a
standard policy of commercial general liability insurance covering, among other
things, Purchaser's indemnification obligation hereunder, naming Seller as an
additional insured, containing coverage limits of not less than $1,000,000,
combined single limit, and written on an occurrence basis. This Section 12(c)
shall survive any termination of this Agreement, and shall not be subject to any
limitation on damages otherwise set forth in this Agreement. If Purchaser
terminates this Agreement pursuant to this Section 12,

                                       23

<PAGE>

then Purchaser shall provide to Seller copies of all appraisals, environmental
studies, surveys, title reports, and any other like materials commissioned by
Purchaser during the Study Period.

          (D) ADDITIONAL INSPECTION. From and after the expiration of the Study
Period, on condition that Purchaser does not terminate this Agreement pursuant
to this Section 12, and subject to subsection (c) hereof, Purchaser and its
agents shall have the right, from time to time, at their own cost and expense,
after reasonable advance notice to Seller and subject to the rights of tenants,
to enter either of the Properties during normal business hours to cause and
perform such additional studies as Purchaser deems reasonably necessary, subject
to the same indemnity by Purchaser specified in subsection (c) hereof.

          (E) REVIEW OF CONTRACTS. During the Study Period, Purchaser shall have
the right to review the Oakton Contracts and the Towngate Contracts, and to
deliver written notification to Seller on or before the Study Period Termination
Date designating one or more of the Oakton Contracts or the Towngate Contracts
to be terminated by Seller on or before the Closing Date; provided, however,
that Purchaser may only designate such Contracts, and Seller shall have the
obligation to terminate only such Contracts, that can be terminated by Seller on
or before the Closing Date without Seller's incurring any penalty or premium.
Seller and Purchaser each confirms and agrees that Purchaser at Closing shall
assume sole liability for the Oakton Contracts and the Towngate Contracts, not
otherwise terminated in accordance with this subsection (e), pursuant to the
provisions of the Oakton General Assignment and the Towngate General Assignment,
as may be applicable. Notwithstanding the foregoing, Purchaser shall not accept
an assignment of, or assume any liability for any property management or any
leasing, listing, or other brokerage agreement, other than in connection with
the World Hope Commission pursuant to Section 7(a)(ix) hereof.

     13. RISK OF LOSS.

          (A) DESTRUCTION OR DAMAGE PRIOR TO CLOSING. If, at any time prior to
the Closing Date, all or any portion of either of the Properties is destroyed or
damaged as a result of fire or any other cause, then Seller shall give written
notice thereof promptly to Purchaser. The rights and obligations of the parties
by reason of such destruction or damage shall be as follows:

               (i) If the "Repair Cost" (as defined below) of such destruction
or damage shall be determined to be Seven Hundred and Fifty Thousand Dollars
($750,000) or less, the Purchase Price shall be deemed reduced by the Repair
Cost and the Oakton Property or the Towngate Property, as may be applicable,
shall be conveyed and accepted in its destroyed or damaged condition. As used in
this Section, the term "Repair Cost" shall mean an estimate obtained by Seller
from a reputable contractor licensed to do business in the Washington, D.C.
metropolitan area, acceptable to Seller's insurance carrier, of the actual cost
of repair and restoration, which estimate is obtained by Seller and delivered to
Purchaser within fifteen (15) days after receiving notice of the destruction or
damage. If Closing is scheduled to occur during said fifteen (15) day period,
Closing shall be delayed to allow Seller the full benefit of said fifteen
(15)-day period. Seller and Purchaser agree that Seller shall be solely entitled
to any insurance proceeds arising under any policy of insurance maintained by
Seller in connection with such destruction or damage, and Purchaser shall
cooperate reasonably with Seller in the recovery of such proceeds.

                                       24

<PAGE>

               (ii) If the Repair Cost of such destruction or damage shall be
determined to exceed Seven Hundred and Fifty Thousand Dollars ($750,000),
Purchaser shall have the option either (1) to accept the Oakton Property or the
Towngate Property, as may be applicable, in its destroyed or damaged condition
and reduce the Purchase Price by the Repair Cost, or (2) to terminate this
Agreement with respect to both Properties by delivering written notification of
such termination to Seller at or before 5 o'clock p.m. (Virginia local time) on
the tenth (10th) day after receiving written notice from Seller of the Repair
Cost. If Closing is scheduled to occur during said ten (10) day period, Closing
shall be delayed to allow Purchaser the full benefit of said ten (10)-day
period. Upon Purchaser's delivery of such notice of termination, this Agreement
shall be deemed terminated; the Deposit and all accrued interest thereon shall
be refunded to Purchaser; and no party shall have any further rights,
liabilities, or obligations in connection with this Agreement, except for those
which may arise under Section 12 (c) hereof. If Purchaser fails to deliver such
written notice of termination in the manner specified above, then Purchaser
shall be deemed to have elected option (1) above, and the sale of the Oakton
Property and the Towngate Property shall be consummated on the earliest
practicable date, as herein provided. If Purchaser elects or is deemed to elect
option (1) above, then Seller and Purchaser agree that Seller shall be solely
entitled to any insurance proceeds arising under any policy of insurance
maintained by Seller in connection with such destruction or damage plus the
amount of any deductible as a credit against the Purchase Price, and Purchaser
shall cooperate reasonably with Seller in the recovery of such proceeds.

          (C) CONDEMNATION. If, prior to the Closing Date, any portion of either
of the Properties shall be condemned or taken pursuant to any governmental or
other power of eminent domain, or any written notice of taking or condemnation
is issued for any portion of the Property, or any proceedings are instituted by
any governmental authority having the power of eminent domain with respect to
any portion of the Oakton Property or the Towngate Property, as may be
applicable, then Seller shall deliver written notification to Purchaser of such
fact promptly after obtaining knowledge thereof. If such condemnation or taking
of a portion of the Oakton Property or the Towngate Property, as may be
applicable, is of such a material nature that, in the reasonable judgment of
Purchaser, it would materially, adversely affect the use and operation of the
Oakton Property or the Towngate Property, as may be applicable, then Purchaser
shall have the right to terminate this Agreement with respect to both Properties
by delivering written notification to Seller at or before 5 o'clock p.m.
(Virginia local time) on the tenth (10th) day after Purchaser's receipt of
Seller's notice. If Closing is scheduled to occur during said ten (10) day
period, Closing shall be delayed to allow Purchaser the full benefit of said ten
(10)-day period. If this Agreement is so terminated, the Deposit and all accrued
interest thereon shall be refunded to Purchaser, and no party shall have any
further rights, liabilities, or obligations in connection with this Agreement,
except for those which may arise under Section 12(c) hereof. If Purchaser does
not terminate this Agreement in the manner specified above, then the sale of the
Property shall be consummated, on the earliest practicable date, as herein
provided at the Purchase Price (without abatement unless Seller has received an
award), and Seller shall assign to Purchaser (without representation or warranty
as to collectibility) at the Closing all of Seller's right, title, and interest
in and to all awards, if any, for the taking, and Purchaser shall be entitled to
receive and keep all awards for the taking of the Oakton Property or the
Towngate Property, as may be applicable, or such portions thereof. If Purchaser
has elected not to terminate this

                                       25

<PAGE>

Agreement, Purchaser shall be entitled to participate in negotiations with the
condemning authority, and Seller shall not compromise, settle, or agree to
accept the amount of any award without Purchaser's prior written consent, which
shall not be unreasonably withheld, conditioned, or delayed. If Purchaser does
not deliver such written notification to Seller timely, it shall be conclusively
presumed that Purchaser has elected not to terminate this Agreement.

     14. BROKERAGE.

          (A) Seller and Purchaser each recognizes Trammel Crow, in its capacity
as Seller's broker (the "Seller's Broker"), as the broker bringing about this
transaction. Seller agrees to pay the Seller's broker a commission pursuant to a
separate agreement; provided that, and on condition that, full and final Closing
occurs under this Agreement. Other than with respect to the Seller's Broker,
each of Purchaser and Seller represents and warrants to the other that it has
not hired, retained, or dealt with any broker, consultant, intermediary, or
finder in connection with the negotiation, execution, or delivery of this
Agreement, or the consummation of the transactions contemplated hereby.

          (B) Seller and Purchaser each covenants and agrees to indemnify the
other against any liability (including without limitation reasonable attorney's
fees and costs of defending same) arising out of any breach of its respective
covenants, representations, or warranties contained in this Section.

     15. FAILURE TO CLOSE.

          (A) PURCHASER'S DEFAULT. In the event that Purchaser shall be in
breach or default of any of its obligations under this Agreement thus
preventing, or otherwise fail to proceed to, Closing in accordance herewith, and
Seller is ready, willing and able to close under this Agreement, then Seller may
terminate this Agreement by delivering written notice thereof to Purchaser, and
shall retain the Deposit (plus any accrued interest thereon), as and for its
sole and exclusive remedy in lieu of all other rights and remedies (including
the right of specific performance), and as Seller's liquidated damages and not
as a penalty, for Purchaser's failure to close and breach of this Agreement, and
Seller, thereafter, shall not have any further liability or obligation to
Purchaser hereunder, nor shall Purchaser have any further liability or
obligation to Seller hereunder, except for any liabilities or obligations
arising under Section 12(c) hereof. Any attendance or appearance at the Closing
by either party shall not nullify or void the provision herein for alternative
performance by payment of liquidated damages as Seller's sole and exclusive
remedy. Seller and Purchaser each agrees that actual damages resulting to Seller
from Purchaser's breach of this Agreement would be difficult or impossible to
measure because of the uncertainties of the real estate market and fluctuations
of property values and differences with respect thereto, and that the Deposit is
a reasonable estimate of damages. In addition, notwithstanding anything to the
contrary in the foregoing, if and in the event that Purchaser has failed to pay
the full amount of the Deposit as calculated in accordance with Section 2 hereof
(including any additional deposits required hereunder), then Seller may pursue
any and all remedies which may be available under law or equity including the
right to compel specific performance and the right to collect damages.

                                       26

<PAGE>

          (B) SELLER'S DEFAULT. In the event that Seller shall be in breach or
default of any of its obligations under this Agreement thus preventing, or
otherwise fail to proceed to, Closing in accordance herewith, and Purchaser is
ready, willing and able to close under this Agreement, then the Deposit and all
accrued interest thereon shall be forthwith returned to Purchaser, and Purchaser
shall have the right to bring suit against Seller either for specific
performance or for reimbursement of Purchaser's actual out-of-pocket damages
reasonably incurred by Purchaser for studies of the Properties undertaken by
Purchaser during the Study Period.

     16. NOTICES. Any notice or other communication required or permitted hereby
(a "Notice") shall be in writing and may be (a) personally delivered with proof
of delivery thereof, or (b) sent by FedEx (or other similar overnight courier),
or (c) sent by United States registered or certified mail, postage prepaid, at a
post office regularly maintained by the United States Postal Service, or (d)
sent by telecopier (with a confirmation copy sent on the same date by FedEx (or
other similar overnight courier), addressed to the respective parties as
follows:

          (a)  if to Seller:

               ELV Associates, Inc.
               70 Long Wharf
               Boston, MA 02110
               Attn: Mr. Scott W. Jenkins
               Telephone No.: 617.589.9444
               Telecopy No.: 617.589.0989

               with copy to:

               Thomas E. Dunigan, Esq.
               Curtin Law Roberson Dunigan & Salans, P.C.
               1900 M Street, NW, Suite 600
               Washington, D.C. 20036
               Telephone No.: 202.530.3300
               Telecopy No.: 202.530.4411

          (c)  if to Purchaser:

               Columbia Equity Trust, Inc.
               1750 H Street, NW, Suite 500
               Washington, DC 20006
               Attn: Clint Fisch
               Telephone No.: 202.303.3080
               Telecopy No.: 202.303.3088

                                       27

<PAGE>

               With a copy to:

               Colin J. Smith, Esq.
               Watt, Tieder, Hoffar & Fitzgerald, L.L.P.
               8405 Greensboro Drive, Suite 100
               McLean, Virginia 22102
               Telephone No.: 703.749.2795
               Telecopy No.: 703.749.0479

          (d)  if to Escrow Agent:

               Commercial Title Group, Inc.
               8605 Westwood Center Drive, Suite 200
               Vienna, Virginia
               Attention: Douglas A. Nichols
               Telephone No.: 703.506.1520
               Telecopy No.: 703.506.9615

Any Notice shall be deemed to have been duly and sufficiently given on the
earliest of the actual receipt of the Notice, the refusal of receipt of the
Notice, or the return of the Notice as undeliverable as a result of a change of
address not communicated to the other parties in accordance herewith. A party
may, by Notice given as aforesaid, change the person or persons and/or address
or addresses for its Notices, provided, however, that a Notice of a change of
addressee or address shall only be effective upon receipt. The giving of a
Notice as a courtesy copy as specified above shall not be a prerequisite to the
effectiveness of any Notice given to a party to this Agreement.

     17. CHOICE OF LAW. The interpretation, enforcement, and performance of this
Agreement shall be governed by the laws of the Commonwealth of Virginia without
regard to the application of choice of law principles.

     18. INDEMNIFICATION GENERALLY.

          (A) SELLER'S INDEMNIFICATION. Seller shall indemnify, defend, and hold
harmless Purchaser, and Purchaser's agents, officers, directors, shareholders,
partners, representatives, employees, consultants, and affiliates, from and
against any and all claims, damages, judgments, liabilities, losses,
settlements, obligations, costs and expenses whatsoever (including without
limitation reasonable attorneys' fees and disbursements) (collectively,
"Losses"), suffered or incurred by, or asserted against, Purchaser and/or any of
such parties, and arising from, relating to, or in connection with (i) the
discovery following Closing of the material breach by Seller of any
representation, warranty, or covenant made by Seller in this Agreement; or (ii)
any obligation under any contract, agreement, or writing entered into by or on
behalf of Seller in respect of the use, construction, operation, ownership,
occupancy, or maintenance of any portion of the Oakton Property or the Towngate
Property, as may be applicable, arising out of any event occurring on or before
the Closing Date; or (iii) any accident, injury, death, or damage caused to any
person or entity or loss of property occurring in or about the Oakton

                                       28

<PAGE>

Property or the Towngate Property, as may be applicable, on or before the
Closing Date, other than claims with respect to which Purchaser is required to
indemnify Seller pursuant to Section 12(c) hereof. Notwithstanding the
foregoing, Seller shall not be liable for any representation which Purchaser
shall have actually known to be untrue prior to Closing, and to which
representation Purchaser shall not have objected prior to Closing.

          (B) PURCHASER'S INDEMNIFICATION. Purchaser shall indemnify, defend,
and hold harmless Seller, and Seller's agents, officers, directors,
shareholders, partners, representatives, employees, consultants, and affiliates,
from and against any and all Losses suffered or incurred by, or asserted
against, Seller and/or any of such parties and arising from, relating to, or in
connection with (i) the discovery following Closing of the material breach by
Purchaser of any representation, warranty, or covenant made by Purchaser in this
Agreement, or (ii) any obligation under any contract, agreement, or writing
entered into by or on behalf of Purchaser in respect of the use, construction,
operation, ownership, occupancy, or maintenance of any portion of the Oakton
Property or the Towngate Property, as may be applicable, arising out of any
event occurring after the Closing Date; or (iii) any accident, injury, death, or
damage caused to any person or entity or loss of property occurring in or about
the Oakton Property or the Towngate Property, as may be applicable, after the
Closing Date. Notwithstanding the foregoing, Purchaser shall not be liable for
any representation which Seller shall have actually known to be untrue prior to
Closing, and to which representation Seller shall not have objected prior to
Closing. The foregoing are in addition to any indemnification obligation of
Purchaser under Section 12(c) hereof.

          (C) SCOPE OF INDEMNIFICATION. Any recovery hereunder shall be limited
to actual damages only (but inclusive of reasonable attorney's fees and costs
whether suit is instituted or not).

          (D) PROCEDURES FOR INDEMNIFICATION. If any action, suit, or proceeding
is commenced, or if any claim, demand, or assessment is asserted, in respect of
which a party is indemnified under this Agreement, or under any agreement or
document delivered pursuant hereto, the indemnified party shall deliver written
notice thereof to the indemnifying party and the indemnifying party shall be
entitled to control the defense, compromise, or settlement thereof, at its own
cost and expense, with counsel reasonably satisfactory to the indemnified party,
and the indemnified party shall cooperate fully with and make available to the
indemnifying party such information under its control or in its possession
relating thereto. The indemnified party may participate in such defense, which
participation shall be at its own cost and expense, unless the indemnified party
reasonably determines that it is not being adequately represented (after notice
to the indemnifying party of such determination and after a reasonable period to
remedy the situation).

     19. SURVIVAL.

          (A) Except as otherwise provided for in this Agreement, all of the
respective obligations of the parties contained in this Agreement or in any
other document delivered in accordance with and pursuant to this Agreement,
including without limitation all covenants, agreements, indemnities,
representations, and warranties, shall survive Closing for a period of

                                       29

<PAGE>

nine (9) months, and shall not be deemed to merge upon the acceptance of
delivery of, or recordation of, the Oakton Deed or the Towngate Deed, as may be
applicable, by Purchaser.

          (B) If, within such nine (9) month period, no written notice is given
by one party to the other party of any alleged breach of a covenant, agreement,
indemnification, representation, or warranty of the other party under this
Agreement, then all liability of the other party, except as may otherwise be
provided in this Agreement, shall terminate. If written notice of any alleged
breach of a covenant, agreement, indemnification, warranty, or obligation is
given to the other party within such nine (9) month period, then the liability
of the other party shall survive as to the matter(s) in question in such notice,
and the liability of the other party as to all other matters shall cease, except
as otherwise provided in this Agreement.

     20. MISCELLANEOUS.

          (A) ENTIRE AGREEMENT; EXHIBITS. This Agreement, together with the
Exhibits and Schedules hereto, constitutes the entire agreement of the parties
hereto regarding the transactions contemplated by this Agreement, and all prior
or contemporaneous agreements, understandings, representations, and statements,
oral or written are hereby merged herein, except for any contemporaneous writing
which expressly states that it is effective notwithstanding this Section 20. The
Exhibits and Schedules attached hereto are hereby incorporated herein and made a
part hereof by reference as fully as though set forth herein.

          (B) AMENDMENTS. This Agreement may not be modified, amended, altered,
supplemented, or canceled except pursuant to the terms hereof or an instrument
in writing signed by the parties hereto.

          (C) PRESS RELEASES. Seller and Purchaser each agrees that, prior to
Closing, neither it, nor its employees, agents, and representatives, will issue
any press release, advertisement, or other public communication with respect to
this Agreement or the transactions contemplated hereby without the prior written
consent of the other party hereto, except to the extent required by law or
governmental regulations or requirements, including without limitation those
applicable to publicly-traded companies.

          (D) BINDING EFFECT. This Agreement does not constitute an offer to
sell and shall not bind either party unless and until each party has executed
and delivered to the other an executed original or faxed counterpart hereof.

          (E) PARTIAL INVALIDITY. If any term or provision of this Agreement or
the application thereof to any person or circumstance shall, to any extent, be
invalid or unenforceable, the remainder of this Agreement, or the application of
such term or provision to persons or circumstances other than those as to which
it is held invalid or unenforceable, shall not be affected thereby, and each
term and provision of this Agreement shall be valid and enforceable to the
fullest extent permitted by law.

          (F) RECORDATION OF AGREEMENT. Neither Seller nor Purchaser may record
this Agreement.

                                       30

<PAGE>

          (G) PREVAILING PARTY COSTS. In the event any dispute between the
parties hereto results in litigation, the prevailing party shall be reimbursed
and indemnified by the party not prevailing in such dispute for all costs and
expenses reasonably incurred by the prevailing party in enforcing or
establishing its rights hereunder, including without limitation court costs and
reasonable attorneys' fees; this provision shall survive Closing.

          (H) HEADINGS; SECTION, EXHIBIT AND SCHEDULE REFERENCES. The Section
headings used herein are for reference purposes only, and do not control or
affect the meaning or interpretation of any term or provision hereof, and shall
not be deemed in any manner to modify, explain, qualify, or restate any of the
provisions of this Agreement. All references in this Agreement to Sections,
Exhibits, and Schedules are to the Sections hereof, and the Exhibits and
Schedules attached hereto, respectively.

          (I) COUNTERPARTS. This Agreement may be executed in any number of
counterparts with the same effect as if all parties hereto had executed the same
document. All such counterparts shall be construed together and shall constitute
one instrument.

          (J) ASSIGNMENT. A party may not assign its respective rights and
obligations hereunder, in whole or in part, without the prior written consent of
the other party, and any assignment without such prior written consent shall be
deemed null and void. This Agreement shall bind and inure to the benefit of the
legal representatives, successors and permitted assigns of the parties hereto.
Notwithstanding the foregoing, Purchaser shall have a one-time right to assign
all (and not less than all) of its rights and obligations hereunder to a third
party upon the following conditions: (i) the assignee shall execute and deliver
to Seller an instrument, in form and substance reasonably acceptable to Seller,
pursuant to which the assignee assumes all of Purchaser's obligations hereunder,
and (ii) such assignment shall not delay the Closing. No such assignment or
transfer shall relieve Purchaser of its liabilities and obligations under this
Agreement.

          (K) NO WAIVER. The failure of any party to enforce at any time any
provision of this Agreement shall not be construed as a waiver of such
provision, or of the right of any party, thereafter, to enforce such provision.
A waiver of any breach of this Agreement shall not be held to be a waiver of any
other or subsequent breach.

          (L) NO OTHER PARTIES. The representations, warranties, and agreements
of the parties contained herein are intended solely for the benefit of the party
to whom such representations, warranties, or agreements are made, and shall not
confer any right hereunder, whether legal or equitable, in any other party, and
no other party shall be entitled to rely thereon.

          (M) CERTAIN DEFINITIONS. Whenever the phrase "final judgment" or
"final non-appealable judgment" or words of similar import are used in this
Agreement or in any other document executed and delivered in connection with the
transaction contemplated herein, such phrase shall be deemed to refer to a
judgment (i) from which no appeal can be taken or (ii) in respect of which the
period for appeal has expired without appeal having been made. Any provision
hereof stated to "survive" Closing shall be deemed not to have been merged into
any deed or bill of sale.

                                       31

<PAGE>

          (N) TIME OF THE ESSENCE. Time is of the essence with respect to all
provisions of this Agreement.

          (O) BUSINESS DAYS. If any date upon which action is required under
this Agreement shall be a Saturday, Sunday, or Federally recognized holiday in
the Commonwealth of Virginia, the date for such action shall be extended to the
first business day after such date that is not a Saturday, Sunday or such legal
HOLIDAY. Unless otherwise specifically provided for herein, any reference to
"days" shall mean and refer to calendar days and not business days.

          (P) EXECUTION BY FACSIMILE. A signed copy of this Agreement or any
amendment hereto or any other document related hereto transmitted by telecopier
or facsimile machine shall be deemed an executed original of such document for
all purposes, and the party so providing such signed copy shall deliver
promptly, thereafter, by nationally recognized overnight courier to all other
parties an executed original copy of such signed document.

     21. ESCROW PROVISIONS.

          (A) The Deposit shall be held in escrow by the Escrow Agent until
Closing or the sooner termination of this Agreement. The Deposit shall be
maintained in an interest-bearing account in a federally insured financial
institution within the Washington D.C. metropolitan area. Interest earned on the
Deposit shall be deemed part of the Deposit and shall be paid to Purchaser or
Seller, as may be the case, in accordance with the other provisions of this
Agreement.

          (B) The Escrow Agent is merely responsible for the safe keeping of the
Deposit and shall not be required to determine any questions of fact or law. In
the event of a dispute between Purchaser and Seller with respect to the
disposition of the Deposit or any interest thereon, the Escrow Agent shall have
no obligation to either Purchaser or Seller except to interplead the Deposit,
together with any interest, in an appropriate court in the Commonwealth of
Virginia, and upon doing so the Escrow Agent shall be relieved of any further
obligation as escrowee.

          (C) The Escrow Agent may act upon any instrument or other writing
believed by it in good faith to be signed and presented by the proper person,
and shall not be liable in connection with the performance by it of its duties
under this Agreement except for its own negligence or willful misconduct. The
Escrow Agent shall not be under any obligation to institute or defend any
action, suit, or legal proceeding in connection herewith, or to take any other
action likely to involve its expense (except to interplead the Deposit as
aforesaid) unless first indemnified to its satisfaction by Purchaser or Seller.

          (D) Seller and Purchaser agree that the Escrow Agent shall have the
right to disburse the Deposit and any accrued interest thereon at the time of
Closing or earlier termination of this Agreement, and that in the event Closing
does not occur for any reason, the Deposit and accrued interest thereon shall be
given or returned by the Escrow Agent to the Seller or Purchaser, as the case
may be, (i) when an "Agreement of Release," in which all parties hereto

                                       32

<PAGE>

authorize and direct the disposition of the Deposit as therein specified, has
been signed by all such parties and delivered to the Escrow Agent, or (ii) as
directed by a court order. If either Seller or Purchaser refuses to execute an
Agreement of Release when requested to do so in writing, and a court finds that
such party should have executed same, the party who so refused to execute an
Agreement of Release shall pay the reasonable expenses, including without
limitation the reasonable attorney's fees and court costs, incurred by the other
party in litigation.

          (E) Seller and Purchaser agree to execute any separate escrow
agreement which the Escrow Agent customarily requires and uses, provided that
such agreement does not materially increase or expand the obligations of either
party as specified in this Agreement.

                            [SIGNATURES ON NEXT PAGE]

                                       33

<PAGE>

     IN WITNESS WHEREOF, each of Seller and Purchaser has caused this Agreement
to be signed as of the Effective Date by its duly authorized representative.

                                        SELLER:

                                        CARFAX ENTERPRISES LIMITED PARTNERSHIP,
                                        A DELAWARE LIMITED PARTNERSHIP

                                        By: E. L. Vaduz Enterprises, Inc.,
                                            a Delaware corporation,
                                            its sole general partner

                                        By: /s/ Scott W. Jenkins
                                            ------------------------------------
                                        Name: Scott W. Jenkins
                                        Title: Vice President

                                        Tax I.D. No. 58-2368752

                                        PURCHASER:

                                        COLUMBIA EQUITY TRUST, INC.
                                        a Maryland corporation

                                        By: /s/ Clint Fisch
                                            ------------------------------------
                                        Name: Clint Fisch
                                        Title: Senior Vice President and
                                               Director of Acq.

                                        Tax I.D. No. 20-1978579

     The Escrow Agent is executing this Agreement to acknowledge the Escrow
Agent's responsibility under this Agreement, which may be modified only by a
written amendment signed by all parties. Any amendment to this Agreement that is
not signed by Escrow Agent shall be effective as to Seller and Purchaser, but
shall not be binding on the Escrow Agent.

                                        ESCROW AGENT

                                        COMMERCIAL TITLE GROUP, INC.

                                        By: /s/ Douglas Nichols
                                            ------------------------------------
                                        Name: Douglas Nichols
                                        Title: President

                                       34
<PAGE>

                                   EXHIBIT A-1
                         DESCRIPTION OF OAKTON PROPERTY

All that certain lot or parcel of land situated, lying and being in Fairfax
County, Virginia and being more particularly described as follows:

All of Parcel B-2-2A as shown on the Plat Showing a Resubdivision of Parcel
"B-2-2", Flint Hill Manor Townhouses, by Dewberry and Davis, C.L.S., dated
February, 1984 (revised August 29, 1984) attached to and as duly dedicated and
recorded by virtue of the Deed of Resubdivision, Deed of Exchange, Deeds of
Partial Release and Amendment of Deeds of Trust and Easement Agreement, dated
June 29, 1984 and recorded in Deed Book 6030 at Page 1707 of the Land Records of
Fairfax County, Virginia.

Said parcel also being shown on and described by metes and bounds according to
As-Built Survey of Carfax Enterprises Limited Partnership Property, prepared for
Carfax Enterprises Limited Partnership, The Manufacturers Life Insurance Company
(U.S.A.), Commonwealth Land Title Insurance Company, and Metropolitan Title
Agency, Inc., dated January 13, 1997, last revised January 29, 1997, prepared by
Bengston, DeBell & Elkins, Ltd., Susan E. Stancik, Commonwealth of Virginia Land
Surveyor, Registration #1818, and more particularly described by metes and
bounds as follows:

Beginning at an iron pipe set at the Southwesterly property corner of the now or
formerly Fairfax Hotel Ltd., Ptp. property, said point lying on the easterly
right-of-way line of Chain Bridge Road, Route 123 (variable width), and being
0.13 miles in a Southerly direction from White Granite Drive; thence South
66 degrees 49' 45" East 413.28 feet with the southerly property line of the now
or formerly Fairfax Hotel Ltd. Ptp. property to an iron pipe set on a westerly
property line of the now or formerly White Granite Associates property; thence,
running with the new or formerly White Granite Associates property the following
courses and distances:

     1. South 23 degrees 11' 16" West 32.73 feet to a set drill hole;

     2. South 66 degrees 48' 44" East 222.00 feet to a set drill hole;

     3. North 75 degrees 09' 33" East 22.19 feet to a found pipe at a northerly
     property corner of Parcel B-2-2B Flint Hill Manor Townhouses; thence
     running with Parcel B-2-2B Flint Mill Manor Townhouses the following
     courses and distances:

     4. South 23 degrees 11' 16" West 37.66 feet to a set PK nail;

     5. North 65 degrees 48' 44" West 310.00 feet to a set PK nail;

     6. South 23 degrees 11' 16" West 214.00 feet to a set drill hole;

     7. North 66 degrees 48' 44" West 13.00 feet to a set drill hole;

     8. South 23 degrees 11' 16" West 43.00 feet to a set PK nail;

<PAGE>

     9. South 66 degrees 48' 44" East 12.00 feet to a set PK nail;

     10. South 23 degrees 11' 16" West 34.00 feet to an iron pipe found;

     11. South 66 degrees 48' 44" East 88.71 feet to an iron pipe found;

     12. South 23 degrees 11' 16" West 29.50 feet to an iron pipe found on the
     northerly property line at Parcel A-l, Section One, Arrowood; thence, North
     66 degrees 40' 44" West 354.56 feet with the northerly property line of
     Parcel A-I, Section One, Arrowood and continuing with the northerly
     property line of the now or formerly Smith property to an iron pipe set on
     the easterly right-of-way line of Chain Bridge Road; thence, running with
     the easterly right-of-way line of Chain Bridge Road the following courses
     and distances:

     13. along the arc of a curve to the right, 700.00 feet in radius, an arc
     distance of 193.87 feet, the chord of said arc running North 08 degrees 46'
     08" East 193.25 feet to an iron pipe set;

     14. North 14 degrees 52' 0l" East 191.96 feet to the point of Beginning and
     containing 129,656 square feet or 2.9765 acres of land, more or less.

Together with a non-exclusive easement of pedestrian ingress and egress as
granted by Oakton II Associates Limited Partnership to Oakton III Associates, a
Virginia limited partnership, by Reciprocal Easement Agreement dated August 6,
1987 and recorded among the Land Records of Fairfax County, Virginia in Deed
Book 6816 at Page 1272.

Also together with an access easement and right of way over and across the
twenty-four foot wide ingress egress easement located on Parcel B-2-2B as
granted by and defined in the Easement Agreement dated September 28, 1984 and
recorded among the Land Records of Fairfax County, Virginia in Deed Book 6041 at
Page 1834.

Also together with easements contained in the Easement and Operating Agreement
dated February 17, 1984 and recorded among the Land Records of Fairfax County,
Virginia in Deed Book 5902 at Page 1374, including the 24 foot wide perpetual
access easement to White Granite Drive as shown on the plat attached to the Deed
of Dedication recorded among the Land Records of Fairfax County, Virginia in
Deed Book 5822 at Page 1, aforesaid records.

Also together with the 6 foot wide perpetual access casement, and the 24 foot
wide ingress egress easement as contained in the Deed of Resubdivision recorded
among the Land Records of Fairfax County, Virginia in Deed Book 6030 at Page
1707.

<PAGE>

Being the land conveyed to CARFAX Enterprises Limited Partnership, a Delaware
limited partnership by Special Warranty Deed recorded January 19, 1995 in Deed
Book 9337 at Page 0850.

Tax Account Number: 047-4-19-B9

<PAGE>

                                   EXHIBIT A-2
                        DESCRIPTION OF TOWNGATE PROPERTY

All that certain lot or parcel of land situated, lying and being in the City of
Alexandria, and being more particularly described as follows:

Lot 503 as shown on the "Plat of Subdivision of the Land of Towngate Associates"
attached to the Deed of Subdivision and Parking Easement recorded in Deed Book
1138 at Page 897 among the Land Records of the City of Alexandria, Virginia.

Together with such easements as may be appurtenant to the property described
herein established by the Deed of Subdivision and Parking Easement recorded in
Deed Book 1138 at Page 897 among the Land Records of the City of Alexandria,
Virginia.

Tax Account Number: 035.04-0402
RPC No. 50449810

<PAGE>

                                   EXHIBIT B-1
                                   OAKTON DEED

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT B-2
                                  TOWNGATE DEED

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT C-1
                               OAKTON BILL OF SALE

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT C-2
                              TOWNGATE BILL OF SALE

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT D-1
                             OAKTON LEASE ASSIGNMENT

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT D-2
                            TOWNGATE LEASE ASSIGNMENT

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT E-1
                            OAKTON GENERAL ASSIGNMENT

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT E-2
                           TOWNGATE GENERAL ASSIGNMENT

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT F-1
                                 TENANT LETTERS

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT F-2
                               CONTRACTOR LETTERS

                              PLEASE SEE ATTACHMENT

<PAGE>

                                    EXHIBIT G
              FOREIGN INVESTMENT IN REAL PROPERTY TAX ACT AFFIDAVIT

                              PLEASE SEE ATTACHMENT

<PAGE>

                                    EXHIBIT H
                             OWNER'S TITLE AFFIDAVIT

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT I-1
                            CC&R ESTOPPEL CERTIFICATE

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT I-2
                              ESTOPPEL CERTIFICATE

                              PLEASE SEE ATTACHMENT
<PAGE>

                                   EXHIBIT J-1
                                  OAKTON LEASES

1.   VANCE INTERNATIONAL, INC. LEASE
     Lease Agreement dated August 22, 1985
     Amendment dated May 1, 1987
     Addendum #2 dated July 22, 1987
     Addendum #3 dated October 26, 1987
     Amendment No. 4 dated January 1,1988
     Amendment No. 5 dated June, 5, 1989
     Sixth Amendment to Lease dated October 31, 1989
     Seventh Amendment to Lease dated September 25, 1991
     Eighth Amendment to Lease dated December 30, 1991
     Ninth Amendment to Lease dated June 15, 1992
     Tenth Amendment to Lease dated May 20, 1993
     Eleventh Amendment to Lease dated November 19, 1993
     Twelfth Amendment to Lease dated March 3, 1994
     Thirteenth Amendment to Lease dated September 27, 1995
     Fourteenth Amendment to Lease dated March 27, 1996
     Fifteenth Amendment to Lease dated April 7, 1997
     Sixteenth Amendment to Lease dated December 7, 1998
     Seventeenth Amendment to Lease dated October 1, 2002
     Eighteenth Amendment to Lease dated September 19, 2003

2.   MRJ, INC. (GENERAL DYNAMICS) LEASE
     Lease Agreement dated February 11, 1991
     First Amendment to Lease dated February 13, 1992
     Second Amendment to Lease dated February 26, 1996
     Third Amendment to Lease dated August 13, 1996
     Fourth Amendment to Lease dated November, 1999
     Fifth Amendment to Lease dated April 12, 2001
     Sixth Amendment to Lease dated March 1, 2005

3.   SUNTRUST MORTGAGE INC. LEASE
     Lease Agreement dated June 30, 2004

                                  II. SUBLEASES

1.   VANCE INTERNATIONAL, INC. LEASE
     Sublease: Decision Strategies LLC dated October 1, 2002

<PAGE>

                                   EXHIBIT J-2
                                 TOWNGATE LEASES

                                    I. LEASES

1.   BACON & THOMAS, PLLC

     Lease Agreement dated September 25, 2001
     First Amendment to Lease dated October 12, 2005

2.   EDO PROFESSIONAL SERVICES, INC. (SUCCESSOR-IN-INTEREST TO DYNAMIC SYSTEMS,
     INC.)

     Lease Agreement dated November 20, 1991
     First Addendum to Lease dated February 22,1993
     Second Amendment to Lease dated October 1, 1996
     Third Amendment to Lease dated April 1, 1997
     Fourth Amendment to Lease dated July 2,1997
     Fifth Amendment to Lease dated November 10,1998
     Sixth Amendment to Lease dated July 9, 2001

3.   AMERICAN ASSOCIATION FOR HOMECARE

     Lease Agreement dated November 1, 1997
     First Amendment to Lease dated May 29, 2001

4.   AMERICAN PUBLIC COMMUNICATIONS COUNCIL, INC.

     Lease Agreement dated February 2, 2004
     First Amendment to Lease dated May 25, 2004

5.   COMMUNITY ANTI-DRUG COALITIONS OF AMERICA

     Lease Agreement dated August 4, 2003
     First Amendment to Lease dated January 26, 2004
     Second Amendment to Lease dated July 22, 2004

6.   CHWAT & COMPANY

     Lease Agreement dated June 14, 2001
     First Amendment to Lease dated February 2, 2004

7.   SUNG EUN KIM

     Lease Agreement dated September 29, 2005

<PAGE>

8.   WORLD HOPE INTERNATIONAL, INC.

     Lease Agreement dated October 29, 2004

                                  II. SUBLEASES

1.   EDO PROFESSIONAL SERVICES, INC. (SUCCESSOR-IN-INTEREST TO DYNAMIC SYSTEMS,
     INC.)

     Dentsply International, Inc. dated September 30, 2003
     Document and Packaging Brokers, Inc. d/b/a DocuPak dated September 25, 2003
     World Hope International, Inc. dated October 18, 2004
     Hatteras Investments, LLC dated February 23,2005

2.   COMMUNITY ANTI-DRUG COALITIONS OF AMERICA

     Acute Long Term Hospital Association dated May 26, 2005

                             III. ACCESS AGREEMENTS

1.   Access to the Towngate Property is permitted, during normal business hours,
     Monday through Friday, to those individuals who are not tenants and who
     possess memberships in the Fitness Center located at Towngate.

<PAGE>

                                    EXHIBIT K
                                SECURITY DEPOSITS

I.   SECURITY DEPOSITS WITH RESPECT TO OAKTON PROPERTY

<TABLE>
<CAPTION>
     TENANT                        CASH AMOUNT
     ------                        -----------
<S>                                <C>
     General Dynamics, Suite 300    $16,874.09
                                    ==========
        TOTAL SECURITY DEPOSITS     $16,874.09
</TABLE>

II.  SECURITY DEPOSITS WITH RESPECT TO TOWNGATE PROPERTY

<TABLE>
<CAPTION>
     TENANT                                                 CASH AMOUNT
     ------                                                 -----------
<S>                                                         <C>
     World Hope International, Suite 100                     $16,729.00
     Chwat & Company, Suite 103                              $ 3,577.00
     American Public Communications Council, Suite 104       $ 7,788.00
     American Association for Homecare, Suite 200            $ 9,601.50
     Community Anti-Drug Coalitions of America, Suite 300    $16,232.00
     Sung Eun Kim, Towngate Cafe, Suite G102                 $   600.00
                                                             ==========
        TOTAL SECURITY DEPOSITS                              $54,527.50
</TABLE>

<PAGE>

                                   EXHIBIT L-1
                                OAKTON RENT ROLL

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT L-2
                               TOWNGATE RENT ROLL

                              PLEASE SEE ATTACHMENT

<PAGE>

                                   EXHIBIT M-1
                       OAKTON LEASING BROKERAGE AGREEMENTS

That certain Exclusive Listing Agreement dated August 16, 2004, by and between
Seller and Trammell Crow Services, Inc.

<PAGE>

                                   EXHIBIT M-2
                      TOWNGATE LEASING BROKERAGE AGREEMENTS

That certain Exclusive Listing Agreement dated August 9, 2004, by and between
Seller and Trammell Crow Services, Inc.

The second installment of that commission due and payable with respect to that
certain Lease Agreement with World Hope International dated October 29, 2004
shall be due and payable on January 1, 2007. The total amount of said second
installment is $16,203.15, and shall be payable as follows: (i) $6,481.27 to be
paid to Trammel Crow Company and (ii) $9,721.89 to be paid to Coldwell Banker
Commercial.

<PAGE>

                                   EXHIBIT N-1
                                OAKTON CONTRACTS

SERVICE CONTRACTS

<TABLE>
<CAPTION>
CONTRACTOR                                         DATE OF CONTRACT
----------                                         ----------------
<S>                                                <C>
American Building Maintenance - Cleaning           11/9/2004
Backflow Technology, LLC - Contractor              N/A
ARC Water Treatment - Cooling Tower                2/1/1995
Chesapeake Protection Services - Sprinkler Tests   5/23/2001
Crystal Window Cleaning                            N/A
Honeywell Security - Security                      11/2/2001
PDS - Waste Management                             11/1/2001
SLS - Landscaping/Flowers/Snow Removal             12/1/2004
ThyssenKrupp Elevator                              11/30/2004
TriStar Mechanical - HVAC Contractor               1/1/2005
Tropical Expressions - Interior Plants             N/A
Western Pest Control                               2/1/1995
</TABLE>

<PAGE>

                                   EXHIBIT N-2
                               TOWNGATE CONTRACTS

SERVICE CONTRACTS

<TABLE>
<CAPTION>
CONTRACTOR                                           DATE OF CONTRACT
----------                                           ----------------
<S>                                                  <C>
ThyssenKrupp Elevator                                11/30/2004
Paradigm Service Group - Sprinkler Tests             12/1/2004
Owl Pest Control                                     5/20/1999
Econo Building Maintenance- Cleaning - Day Porter    9/29/2003
GSHall - Engineering & HVAC Maintenance              7/20/2004
Kastle Systems - Security Monitoring & Maintenance   12/18/2001
Crystal Window Cleaning                              N/A
Tropical Expressions - Interior Plants               N/A
</TABLE>

COST SHARING AGREEMENT

Cost Sharing Agreement dated December 31, 2002, and effective January 1, 2002,
by and between Seller and Towngate IV, L.L.C.

<PAGE>

                                   EXHIBIT O-1
                                 OAKTON PERMITS

                                      NONE

<PAGE>

                                   EXHIBIT O-2
                                TOWNGATE PERMITS

                                      NONE

<PAGE>

                                    EXHIBIT P
                                 TAX PROCEEDINGS

                                      NONE

<PAGE>

                                    EXHIBIT Q
                                  TI ALLOWANCES

OAKTON PROPERTY

Vance International:        $ 21,965.30

TOWNGATE PROPERTY

World Hope International:   $38,048.00
Bacon & Thomas:             $47,375.00<PAGE>

                                                                   Exhibit 10.17

                      FIRST AMENDMENT TO AGREEMENT OF SALE

     THIS FIRST AMENDMENT TO AGREEMENT OF SALE (the "First Amendment") is made
as of the 23rd day of November, 2005, by and between CARFAX ENTERPRISES LIMITED
PARTNERSHIP, a Virginia limited partnership ("Seller"), and COLUMBIA EQUITY
TRUST, INC., a Maryland corporation ("Purchaser").

                                    RECITALS:

     R-1. Seller and Purchaser are parties to that certain Agreement of Sale
having an Effective Date of November 10, 2005 (the "Agreement of Sale") for the
sale and purchase of the Properties as specified and defined therein (all
capitalized terms not otherwise defined herein shall have the respective
meanings set forth in the Agreement of Sale).

     R-2. Seller and Purchaser have agreed to certain amendments to the
Agreement of Sale subject to and in accordance with the terms and provisions of
this First Amendment.

     NOW, THEREFORE, in consideration of the mutual promises set forth herein
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, the parties agree as follows:

     1. Seller and Purchaser each acknowledges and agrees that the original
intent of the parties as evidenced in the Agreement of Sale was to consummate
the transactions contemplated in the Agreement of Sale with respect to the
Oakton Property and the Towngate Property on a joint contemporaneous basis.
Seller and Purchaser now have agreed that the transaction contemplated in the
Agreement of Sale with respect to the Oakton Property and the transaction
contemplated in the Agreement of Sale with respect to the Towngate Property
shall be consummated separately subject to and in accordance with the terms and
provisions of the Agreement of Sale applicable to each of the Oakton Property
and the Towngate Property. Seller and Purchaser each confirms and agrees that
all of the terms and provisions of the Agreement of Sale shall be interpreted so
as to effectuate the foregoing intent and agreement of the parties to the
fullest extent possible. In furtherance and not in limitation of the foregoing,
Seller and Purchaser each specifically agrees (a) that occurrence of the "Oakton
Closing" (as hereinafter defined) and the "Towngate Closing" (as hereinafter
defined) shall not in any manner be related to or conditioned upon the
occurrence of the other Closing; (b) that Purchaser, by consummating the Oakton
Closing, shall not thereby have any obligation to consummate the Towngate
Closing; and (c) that in the event Purchaser exercises its right under Section
12(b) of the Agreement of Sale to terminate the Agreement of Sale with respect
to the Oakton Property on or before the Oakton Study Period Termination Date,
then Seller shall have the right to terminate the Agreement of Sale with respect
to the Towngate Property by delivering written notice of such termination within
three business days of Seller's receipt of Purchaser's termination notice under
Section 12(b), in which event the Towngate Deposit and all accrued interest
thereon shall be refunded to Purchaser, and no party shall have any further
rights, liabilities, or obligations in connection with the Agreement of Sale
with respect to the Towngate Property, except for those which may arise under
Section 12(c) of the Agreement of Sale with respect to the Towngate Property.
All references in the Agreement of Sale to "Properties" shall be deemed to mean
and

<PAGE>

refer to each of the Oakton Property and the Towngate Property, as may be
applicable and as the context may require.

     2. Section 2 of the Agreement of Sale is hereby deleted in its entirety and
the following new Section 2 is hereby inserted in lieu thereof:

          "2.  PRICE AND PAYMENT.

               (A) The aggregate purchase price for the Properties shall be the
sum of TWENTY-SIX MILLION EIGHT HUNDRED FIFTY THOUSAND AND 00/100 DOLLARS
($26,850,000.00) (the "Purchase Price"). The Purchase Price shall be allocated
between the Properties as follows: SIXTEEN MILLION AND 00/100 DOLLARS
($16,000,000.00) as and for the purchase price for the Oakton Property (the
"Oakton Purchase Price"), and TEN MILLION EIGHT HUNDRED FIFTY THOUSAND AND
00/100 DOLLARS ($10,850,000.00) as and for the purchase price for the Towngate
Property (the "Towngate Purchase Price").

               (B) The Oakton Purchase Price shall be payable as follows:

                    (i) Not later than 5:00 o'clock p.m. (local Virginia time)
on the second business day following the full execution of this Agreement by
Seller and Purchaser, Purchaser shall deliver, or cause to be delivered, the sum
of ONE HUNDRED TWENTY THOUSAND AND 00/100 DOLLARS ($120,000.00) (the "Oakton
Initial Deposit"), by wire transfer of immediately available federal funds
actually received, to Commercial Title Group, 8605 Westwood Center Drive, Suite
200, Vienna, Virginia 22182 (the "Escrow Agent" or the "Settlement Agent").

                    (ii) On condition that this Agreement is not terminated by
Purchaser with respect to the Oakton Property in accordance with Section 12
hereof, Purchaser, not later than 5:00 o'clock p.m. (local Virginia time) on the
second business day following the Oakton Study Period Termination Date (as
defined in Section 12(a) hereof), shall increase the Oakton Initial Deposit to
SIX HUNDRED THOUSAND AND 00/100 DOLLARS ($600,000.00) by delivering to the
Escrow Agent an additional deposit (the "Oakton Additional Deposit") in the
amount of FOUR HUNDRED EIGHTY THOUSAND AND 00/100 DOLLARS ($480,000.00), in the
form of immediately available federal funds actually received (the Oakton
Initial Deposit and the Oakton Additional Deposit being hereinafter referred to
as the "Oakton Deposit").

                    (iii) If Purchaser exercises its option to extend the Oakton
Closing Date for up to an additional thirty (30) days in accordance with Section
3 hereof, then Purchaser, not later than 5:00 o'clock p.m. (local Virginia time)
on the second business day following the "Oakton Closing Extension Date" as
defined in Section 3 hereof, shall increase the Oakton Deposit to NINE HUNDRED
THOUSAND AND 00/100 DOLLARS ($900,000.00) by delivering to the Escrow Agent an
additional deposit (the "Oakton Extension Deposit") in the amount of THREE
HUNDRED THOUSAND AND 00/100 DOLLARS ($300,000.00), in the form of immediately
available federal funds actually received (the Oakton Deposit and the Oakton
Extension Deposit being hereinafter referred to as the "Oakton Deposit").
References in

                                        2

<PAGE>

all other provisions of this Agreement to the "Deposit" shall be deemed to mean
and refer to the Oakton Deposit as may be applicable and as the context may
require.

                    (iv) On condition that this Agreement is not terminated by
Purchaser in accordance with Section 12 hereof, the Oakton Deposit shall be
non-refundable, except as specifically provided for in Section 15(b) hereof or
elsewhere in this Agreement.

                    (v) The balance of the Oakton Purchase Price (the "Oakton
Purchase Price Balance"), after taking into account the Oakton Deposit under and
pursuant to this Section 2, and subject to prorations and adjustments as
provided for in this Agreement, shall be paid by Purchaser at the "Oakton
Closing" (as hereinafter defined) by wire transfer of immediately available
federal funds actually received and credited to the account of the Settlement
Agent to be designated by it in writing prior to the Oakton Closing.

               (C) The Towngate Purchase Price shall be payable as follows:

                    (i) Not later than 5:00 o'clock p.m. (local Virginia time)
on the second business day following the full execution of this Agreement by
Seller and Purchaser, Purchaser shall deliver, or cause to be delivered, the sum
of EIGHTY THOUSAND AND 00/100 DOLLARS ($80,000.00) (the "Towngate Initial
Deposit"), by wire transfer of immediately available federal funds actually
received, to the Escrow Agent.

                    (ii) On condition that this Agreement is not terminated by
Purchaser with respect to the Towngate Property in accordance with Section 12
hereof, Purchaser, not later than 5:00 o'clock p.m. (local Virginia time) on the
second business day following the Towngate Study Period Termination Date (as
defined in Section 12(a) hereof), shall increase the Towngate Initial Deposit to
FOUR HUNDRED THOUSAND AND 00/100 DOLLARS ($400,000.00) by delivering to the
Escrow Agent an additional deposit (the "Towngate Additional Deposit") in the
amount of THREE HUNDRED TWENTY THOUSAND AND 00/100 DOLLARS ($320,000.00), in the
form of immediately available federal funds actually received (the Towngate
Initial Deposit and the Towngate Additional Deposit being hereinafter referred
to as the "Towngate Deposit").

                    (iii) If Purchaser exercises its option to extend the
Towngate Closing Date for up to an additional thirty (30) days in accordance
with Section 3 hereof, then Purchaser, not later than 5:00 o'clock p.m. (local
Virginia time) on the second business day following the "Towngate Closing
Extension Date" as defined in Section 3 hereof, shall increase the Towngate
Deposit to SIX HUNDRED THOUSAND AND 00/100 DOLLARS ($600,000.00) by delivering
to the Escrow Agent an additional deposit (the "Towngate Extension Deposit") in
the amount of TWO HUNDRED THOUSAND AND 00/100 DOLLARS ($200,000.00), in the form
of immediately available federal funds actually received (the Towngate Deposit
and the Towngate Extension Deposit being hereinafter referred to as the
"Towngate Deposit"). References in all other provisions of this Agreement to the
"Deposit" shall be deemed to mean and refer to the Towngate Deposit as may be
applicable and as the context may require.

                                        3

<PAGE>

                    (iv) On condition that this Agreement is not terminated by
Purchaser in accordance with Section 12 hereof, the Towngate Deposit shall be
non-refundable, except as specifically provided for in Section 15(b) hereof or
elsewhere in this Agreement.

                    (v) The balance of the Towngate Purchase Price (the
"Towngate Purchase Price Balance"), after taking into account the Towngate
Deposit under and pursuant to this Section 2, and subject to prorations and
adjustments as provided for in this Agreement, shall be paid by Purchaser at the
"Towngate Closing" (as hereinafter defined) by wire transfer of immediately
available federal funds actually received and credited to the account of the
Settlement Agent to be designated by it in writing prior to the Towngate
Closing.

               (D) The Settlement Agent shall hold any and all deposits received
under this Section 2 in escrow in accordance with and pursuant to the provisions
of Section 21 hereof. For the purposes of the interest-bearing account specified
in Section 21, Purchaser's tax identification number is set forth below
Purchaser's signature hereto.

               (E) References in all other provisions of this Agreement to the
"Purchase Price Balance" shall be deemed to mean and refer to the Oakton
Purchase Price Balance or the Towngate Purchase Price Balance, as may be
applicable and as the context may require."

     3. Section 3 of the Agreement of Sale is hereby deleted in its entirety and
the following new Section 3 is hereby inserted in lieu thereof:

          "3.  CLOSING.

               (A) Subject to the other applicable provisions of this Agreement
and to the immediately succeeding sentence, closing of the transactions
contemplated hereby with respect to the Oakton Property (the "Oakton Closing")
shall occur at the offices of the Settlement Agent at 10:00 a.m. on the tenth
(10th) business day following the Oakton Study Period Termination Date as
defined in Section 12 hereof, or if that day is not a business day, then on the
immediately succeeding business day, or on such other day, or at such other time
or place as may be otherwise agreed upon by Seller and Purchaser in their
respective sole discretion. Purchaser shall have the option to extend the date
for the Oakton Closing for up to a maximum period of thirty (30) days provided
that and on specific condition that Purchaser (i) delivers to Seller on a date
(the "Oakton Closing Extension Date") not later than three (3) business days
prior to the originally scheduled date for the Oakton Closing a written notice
exercising such option and specifying the new date for the Oakton Closing, and
(ii) delivers to the Escrow Agent on or before the Oakton Closing Extension Date
the Oakton Extension Deposit in accordance with Section 2 hereof. The term
"Oakton Closing Date," as used in this Agreement, shall mean the date when the
transactions contemplated hereunder with regard to the Oakton Property are
consummated.

               (B) Subject to the other applicable provisions of this Agreement
and to the immediately succeeding sentence, closing of the transactions
contemplated hereby with respect to the Towngate Property (the "Towngate
Closing") shall occur at the offices of the

                                        4

<PAGE>

Settlement Agent at 10:00 a.m. on the tenth (10th) business day following the
Towngate Study Period Termination Date as defined in Section 12 hereof, or if
that day is not a business day, then on the immediately succeeding business day,
or on such other day, or at such other time or place as may be otherwise agreed
upon by Seller and Purchaser in their respective sole discretion. Purchaser
shall have the option to extend the date for the Towngate Closing for up to a
maximum period of thirty (30) days provided that and on specific condition that
Purchaser (i) delivers to Seller on a date (the "Towngate Closing Extension
Date") not later than three (3) business days prior to the originally scheduled
date for the Towngate Closing a written notice exercising such option and
specifying the new date for the Towngate Closing, and (ii) delivers to the
Escrow Agent on or before the Towngate Closing Extension Date the Towngate
Extension Deposit in accordance with Section 2 hereof. The term "Towngate
Closing Date," as used in this Agreement, shall mean the date when the
transactions contemplated hereunder with regard to the Towngate Property are
consummated.

               (C) References in all other provisions of this Agreement to (i)
the "Closing" shall be deemed to mean and refer to the Oakton Closing or the
Towngate Closing, as may be applicable and as the context may require, and (ii)
the "Closing Date" shall be deemed to mean and refer to the Oakton Closing Date
or the Towngate Closing Date, as may be applicable and as the context may
require."

     4. With respect to Section 6 of the Agreement of Sale, Seller and Purchaser
each agrees, and Section 6 shall be deemed amended, as follows:

          (A) Purchaser's obligation to pay the Oakton Purchase Price Balance,
to accept title to the Oakton Property, and otherwise to consummate the
transactions with respect to the Oakton Property contemplated by the Agreement
of Sale shall be subject to the satisfaction, on and as of the Oakton Closing
Date (except with respect to Section 6(a)(iv) which shall be satisfied within
the time period specified therein), of the conditions precedent specified in
Section 6(a) of the Agreement of Sale specifically related to the Oakton
Property. Seller's obligation to deliver title to the Oakton Property and to
otherwise consummate the transactions with respect to the Oakton Property
contemplated by the Agreement of Sale shall be subject to compliance by
Purchaser with the conditions precedent specified in Section 6(b) of the
Agreement of Sale specifically related to the Oakton Property on and as of the
Oakton Closing Date.

          (B) Purchaser's obligation to pay the Towngate Purchase Price Balance,
to accept title to the Towngate Property, and otherwise to consummate the
transactions with respect to the Towngate Property contemplated by the Agreement
of Sale shall be subject to the satisfaction, on and as of the Towngate Closing
Date (except with respect to Section 6(a)(iv) which shall be satisfied within
the time period specified therein), of the conditions precedent specified in
Section 6(a) of the Agreement of Sale specifically related to the Towngate
Property. Seller's obligation to deliver title to the Towngate Property and to
otherwise consummate the transactions with respect to the Towngate Property
contemplated by the Agreement of Sale shall be subject to compliance by
Purchaser with the conditions precedent specified in Section 6(b) specifically
related to the Towngate Property on and as of the Towngate Closing Date.

                                        5

<PAGE>

     5. With respect to Section 7 of the Agreement of Sale, Seller and Purchaser
each agrees, and Section 7 shall be deemed amended, as follows:

          (A) The representations and warranties of Seller contained in Section
7 of the Agreement of Sale, insofar as said representations and warranties
relate to Seller and/or the Oakton Property, shall be true and correct in all
material respects as of the Effective Date and as of the Oakton Closing Date.

          (B) The representations and warranties of Seller contained in Section
7 of the Agreement of Sale, insofar as said representations and warranties
relate to Seller and/or the Towngate Property, shall be true and correct in all
material respects as of the Effective Date and as of the Towngate Closing Date.

     6. Section 12(a) and Section 12(b) of the Agreement of Sale each is hereby
deleted in its entirety and the following new Section 12(a) and Section 12(b)
each is hereby inserted in lieu thereof:

          "(A) LENGTH OF STUDY PERIOD.

               (i) During that period (the "Oakton Study Period") commencing as
of the Effective Date, and ending at 5:00 o'clock p.m. (Virginia local time) on
November 30, 2005 (the "Oakton Study Period Termination Date"), Purchaser, and
its employees, consultants, engineers, agents, and representatives, at
Purchaser's sole cost and expense, shall have the right, subject to subsection
(c) hereof, to conduct such feasibility studies of the Oakton Property,
including without limitation architectural, engineering, environmental,
hydrologic, zoning, and development and economic feasibility studies and
investigations; audits of the books and records of Seller reasonably related to
the Oakton Property; and conferences with governmental staff members and the
Oakton Tenants (collectively, the "Oakton Feasibility Studies") as Purchaser
deems necessary; provided, however, that Purchaser shall not be permitted to
undertake any soil borings or other drillings on the Oakton Property without
prior written notice to, and consent of, Seller. Seller shall cooperate
reasonably with Purchaser and its agents in permitting Purchaser and its agents
full access to the Oakton Property, and all books, records, files, financial
data relating to the Oakton Property, and the Oakton Leases and the Oakton
Contracts, to conduct the Oakton Feasibility Studies. Such access shall be
during normal business hours, after the giving of reasonable advance notice to
Seller, and subject to the rights of tenants. Purchaser, and its employees,
consultants, engineers, agents, and representatives, shall use reasonable and
diligent efforts to minimize interference with the management, operation, use,
or maintenance of any portion of the Oakton Property by Seller and its tenants,
agents, contractors, and employees. The parties acknowledge that Purchaser may
be required to perform a historical audit of the Oakton Property in order to
comply with Item 3-14 of Regulation S-X promulgated under the Securities Act of
1933 and the Securities Exchange Act of 1934. Seller shall, during the time
period for which access is allowed hereunder, take commercially reasonable
efforts to permit Purchaser's auditors access at that location where Seller
customarily maintains its records, upon reasonable advance notice and during
normal business hours, to all of the Oakton Property's books and records and the
operating statements (certified by an officer of the general partner of Seller)
and property management balance sheets for the Oakton Property for three (3)
calendar years prior to

                                        6

<PAGE>

the Oakton Closing Date. To the extent that the originals or copies of same are
not otherwise provided by Seller to Purchaser at the Oakton Closing, and to the
extent that the same are ordinarily maintained by Seller in its normal course of
business, such books and records shall include the detail general ledger of
profits and loss, accounts receivable records, and rent rolls. Buyer's access
rights shall commence on the Effective Date and shall continue until the earlier
to occur of (i) the termination of this Agreement with respect to the Oakton
Property by either Seller or Purchaser in accordance with the terms of this
Agreement or (ii) the successful completion of the audit and the filing of the
3-14 report with the SEC, written notice of which shall be delivered promptly by
Purchaser to Seller. The foregoing obligation shall fully survive the Oakton
Closing. Notwithstanding anything to the contrary in the foregoing, other than
providing the access to Purchaser specified herein, Seller shall not have any
liability or responsibility in connection with or in any manner related to,
directly or indirectly, any audit required to be made by Purchaser or any
compliance required of Purchaser with any Regulation under the Securities Act of
1933 or the Securities Act of 1934.

               (ii) During that period (the "Towngate Study Period") commencing
as of the Effective Date, and ending at 5:00 o'clock p.m. (Virginia local time)
on December 9, 2005 (the "Towngate Study Period Termination Date"), Purchaser,
and its employees, consultants, engineers, agents, and representatives, at
Purchaser's sole cost and expense, shall have the right, subject to subsection
(c) hereof, to conduct such feasibility studies of the Towngate Property,
including without limitation architectural, engineering, environmental,
hydrologic, zoning, and development and economic feasibility studies and
investigations; audits of the books and records of Seller reasonably related to
the Towngate Property; and conferences with governmental staff members and the
Towngate Tenants (collectively, the "Towngate Feasibility Studies") as Purchaser
deems necessary; provided, however, that Purchaser shall not be permitted to
undertake any soil borings or other drillings on the Towngate Property without
prior written notice to, and consent of, Seller. Seller shall cooperate
reasonably with Purchaser and its agents in permitting Purchaser and its agents
full access to the Towngate Property, and all books, records, files, financial
data relating to the Towngate Property, and the Towngate Leases and the Towngate
Contracts, to conduct the Towngate Feasibility Studies. Such access shall be
during normal business hours, after the giving of reasonable advance notice to
Seller, and subject to the rights of tenants. Purchaser, and its employees,
consultants, engineers, agents, and representatives, shall use reasonable and
diligent efforts to minimize interference with the management, operation, use,
or maintenance of any portion of the Towngate Property by Seller and its
tenants, agents, contractors, and employees. The parties acknowledge that
Purchaser may be required to perform a historical audit of the Towngate Property
in order to comply with Item 3-14 of Regulation S-X promulgated under the
Securities Act of 1933 and the Securities Exchange Act of 1934. Seller shall,
during the time period for which access is allowed hereunder, take commercially
reasonable efforts to permit Purchaser's auditors access at that location where
Seller customarily maintains its records, upon reasonable advance notice and
during normal business hours, to all of the Towngate Property's books and
records and the operating statements (certified by an officer of the general
partner of Seller) and property management balance sheets for the Towngate
Property for three (3) calendar years prior to the Towngate Closing Date. To the
extent that the originals or copies of same are not otherwise provided by Seller
to Purchaser at the Towngate Closing, and to the extent that the same are
ordinarily maintained by Seller in its normal course of business, such books and
records shall

                                        7

<PAGE>

include the detail general ledger of profits and loss, accounts receivable
records, and rent rolls. Buyer's access rights shall commence on the Effective
Date and shall continue until the earlier to occur of (i) the termination of
this Agreement with respect to the Towngate Property by either Seller or
Purchaser in accordance with the terms of this Agreement or (ii) the successful
completion of the audit and the filing of the 3-14 report with the SEC, written
notice of which shall be delivered promptly by Purchaser to Seller. The
foregoing obligation shall fully survive the Towngate Closing. Notwithstanding
anything to the contrary in the foregoing, other than providing the access to
Purchaser specified herein, Seller shall not have any liability or
responsibility in connection with or in any manner related to, directly or
indirectly, any audit required to be made by Purchaser or any compliance
required of Purchaser with any Regulation under the Securities Act of 1933 or
the Securities Act of 1934.

               (iii) References in all other provisions of this Agreement to the
"Study Period Termination Date" shall be deemed to mean and refer to the Oakton
Study Period Termination Date or the Towngate Study Period Termination Date, as
may be applicable and as the context may require.

          (B) PURCHASER'S TERMINATION.

               (i) Purchaser shall have the right, for any reason or no reason
at all, to terminate this Agreement with respect to the Oakton Property by
delivering to Seller written notice of such termination at or before 5 o'clock
p.m. (Virginia local time) on the Oakton Study Period Termination Date. If
Purchaser terminates this Agreement with respect to the Oakton Property in the
manner set forth above, then the Oakton Deposit and all accrued interest thereon
shall be refunded to Purchaser, and no party shall have any further rights,
liabilities, or obligations in connection with this Agreement with respect to
the Oakton Property, except for those which may arise under subsection (c)
hereof. If Purchaser does not terminate this Agreement with respect to the
Oakton Property in the manner set forth above, then this Agreement shall remain
and continue in full force and effect with respect to the Oakton Property.

               (ii) Purchaser shall have the right, for any reason or no reason
at all, to terminate this Agreement with respect to the Towngate Property by
delivering to Seller written notice of such termination at or before 5 o'clock
p.m. (Virginia local time) on the Towngate Study Period Termination Date. If
Purchaser terminates this Agreement with respect to the Towngate Property in the
manner set forth above, then the Towngate Deposit and all accrued interest
thereon shall be refunded to Purchaser, and no party shall have any further
rights, liabilities, or obligations in connection with this Agreement with
respect to the Towngate Property, except for those which may arise under
subsection (c) hereof. If Purchaser does not terminate this Agreement with
respect to the Towngate Property in the manner set forth above, then this
Agreement shall remain and continue in full force and effect with respect to the
Towngate Property."

     7. This First Amendment may be executed in any number of counterparts, each
of which shall constitute one and the same instrument, and each party hereto may
execute this First Amendment by signing any such counterpart. Any facsimile
signature to this First Amendment shall be deemed an original for purposes of
determining the enforceability of this First

                                        8

<PAGE>

Amendment, and either party providing such facsimile signature shall deliver
promptly, thereafter, by nationally recognized overnight courier to the other
party an executed original copy of this First Amendment.

     8. The Agreement of Sale, as amended by this First Amendment, is and shall
remain in full force and effect.

                            [SIGNATURES ON NEXT PAGE]

                                        9

<PAGE>

          IN WITNESS WHEREOF, each of Seller and Purchaser has caused this First
Amendment to be executed by its duly authorized representative as of the
effective date first above written.

                                        SELLER:

                                        CARFAX ENTERPRISES LIMITED PARTNERSHIP,
                                        A DELAWARE LIMITED PARTNERSHIP

                                        By: E. L. Vaduz Enterprises, Inc.,
                                            a Delaware corporation,
                                            its sole general partner

                                        By: /s/ Scott W. Jenkins
                                            ------------------------------------
                                        Name: Scott W. Jenkins
                                        Title: Vice President

                                        PURCHASER:

                                        COLUMBIA EQUITY TRUST, INC.,
                                        a Maryland corporation

                                        By: /s/ Clint Fisch
                                            ------------------------------------
                                        Name: Clint Fisch
                                        Title: Senior Vice President

The Escrow Agent is executing this First Amendment to acknowledge the Escrow
Agent's responsibility under this First Amendment, which may be modified only by
a written amendment signed by all parties.

                                        ESCROW AGENT:

                                        COMMERCIAL TITLE GROUP, INC.

                                        By: /s/ Douglas Nichols
                                            ------------------------------------
                                        Name: Douglas Nichols
                                        Title: President

                                       10

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