Question: who suggested in 1973 that it was on this drive that Wood first sketched the house on the back of an envelope
About the article "American Gothic", section "Creation".

Candidate passages:
In August 1930, Grant Wood, an American painter with European training, was driven around Eldon, Iowa by a young painter from Eldon, John Sharp, looking for inspiration.
Wood noticed the Dibble House, a small white house built in the Carpenter Gothic architectural style.
Sharp's brother suggested in 1973 that it was on this drive that Wood first sketched the house on the back of an envelope.
Wood's earliest biographer, Darrell Garwood, noted that Wood "thought it a form of borrowed pretentiousness, a structural absurdity, to put a Gothic-style window in such a flimsy frame house."
At the time, Wood classified it as one of the "cardboardy frame houses on Iowa farms" and considered it "very paintable".
After obtaining permission from the Jones family, the house's owners, Wood made a sketch the next day in oil on paperboard from the house's front yard.
This sketch displayed a steeper roof and a longer window with a more pronounced ogive than on the actual house, features which eventually adorned the final work.
Wood decided to paint the house along with "the kind of people I fancied should live in that house."
He recruited his sister Nan (1899–1990) to model the woman, dressing her in a colonial print apron mimicking 19th-century Americana.
The man is modeled on Wood's dentist, Dr. Byron McKeeby (1867–1950) from Cedar Rapids, Iowa.
The three-pronged hay fork is echoed in the stitching of the man's overalls, the Gothic window of the house, and the structure of the man's face.
However, Wood did not add figures to his sketch until he returned to his studio in Cedar Rapids.
He would not return to Eldon again before his death in 1942, although he did request a photograph of the home to complete his painting.
During the summer of 1930, Edward Rowan, a young gallery director from Cedar Rapids, a large city approximately to the northwest of Eldon, attempted to promote fine arts in the rural town by opening a gallery and library and leading art classes in Eldon.
Rowan's attempts were met with success—the "Eldon Forum" called the exhibitions "an unusual treat."
This, along with an indebtedness Wood felt toward Rowan, drew the painter (himself a native of Anamosa, Iowa) to come to Eldon.
In August, Wood was driven around the town by a young painter from Eldon, John Sharp, looking for inspiration.
Sharp's brother suggested in 1973 that it was on this drive that Wood first sketched the house on the back of an envelope.
Wood did not immediately regard the house as beautiful, but he did find it captivating.
His earliest biographer, Darrell Garwood, noted that Wood "thought it a form of borrowed pretentiousness, a structural absurdity, to put a Gothic-style window in such a flimsy frame house."
At the time, Wood classified it as one of the "cardboardy frame houses on Iowa farms" and considered it "very paintable."
After obtaining the permission of the Jones family, Wood made a sketch the next day in oil on paperboard from the house's front yard.
This sketch displayed a steeper roof and a longer window with a more pronounced ogive than the actual house, features which eventually adorned the final work; however, Wood did not add figures to the sketch until he returned to Cedar Rapids.
He would not return to Eldon again before his death in 1942, although he did request a photograph of the home to complete his painting. 
In December 2009 an envelope containing suspicious white powder was sent to Malik's office at the House of Commons, triggering an anti-terrorist investigation.
Comments written on the envelope suggested it had been sent by a supporter of the far-right.
The substance was later found to be harmless. 
The pavilion had 2 floors, and the bottom floor may have been used at one stage as a kitchen for the preparation of refreshments for the ladies and gentlemen who came down from Bonnington House to view the falls.
A relatively large window, probably originally having shutters either side, looks onto the falls.
The entrance door has a window set on each side, which would have prevented the projection of an image onto mirrors placed onto this 'back' wall.
A window and ground floor door were present in each of the two side walls of the building; providing up to three doors altogether into the ground floor and a total of five windows, providing for exceptionally good views out of the building.
The only apparently uninterrupted surface was the upper ceiling.
The artist Alexander Archer sketched the pavilion, probably including some 'artistic licence' from the south-west in 1837.
This sketch shows a different arrangement of the steps leading up to the door and a stone gable end, with highly ornate 'crow step' ornamentation, which would have given the building a typical arched sloping roof rather than a flat one as suggested by the remains today (2007).
It may well be that the changes to the entrance steps took place when the hydroelectric power station was constructed in 1926 as the pipes carrying the water to the turbine house run very close to the pavilion entrance and they had to be moved to run parallel to the front of the building.
The building shows signs of other alterations, such as the closing up of one of the lower ground front 'servants' entrance to the suggested kitchen area and the provision of a balustrade at the viewing window, suggesting that at a later date the method of use of the building changed.
Some modern repairs have been carried out to stabilise the building as indicated by recent pointing work, new wood lintels, etc. 
Assume without loss of generality that the support of the distribution of interest, formula_2, is contained in <math> Given a confidence envelope for formula_2, it can be shown that the CDF within the envelope that minimizes the variance begins on the lower envelope, has a jump continuity to the upper envelope, and then continues along the upper envelope.
Further, it can be shown that this variance-minimizing CDF, F', must satisfy the constraint that the jump discontinuity occurs at formula_17.
The variance maximizing CDF begins on the upper envelope, horizontally transitions to the lower envelope, then continues along the lower envelope.
Explicit algorithms for calculating these variance-maximizing and minimizing CDFs are given by Romano and Wolf.