Accounts Receivable, net
## Table 0 ##
The increase in accounts receivable was primarily due to the increased billings during the fiscal year ended October 31, 2006.
Days sales outstanding (DSO) was 39 days at October 31, 2006 and 36 days at October 31, 2005.
Our accounts receivable and DSO are primarily driven by our billing and collections activities.
Net Working Capital Working capital is comprised of current assets less current liabilities, as shown on our balance sheet.
As of October 31, 2006, our working capital was $23.4 million, compared to $130.6 million as of October 31, 2005.
The decrease in net working capital of $107.2 million was primarily due to (1) a decrease of $73.7 million in cash and cash equivalents; (2) a decrease of current deferred tax assets of $83.2 million, primarily due to a tax accounting method change; (3) a decrease in income taxes receivable of $5.8 million; (4) an increase in income taxes payable of $21.5 million; (5) an increase in deferred revenue of $29.9 million; and (6) a net increase of $2.8 million in accounts payable and other liabilities which included a reclassification of debt of $7.5 million from long term to short term debt.
This decrease was partially offset by (1) an increase in short-term investments of $59.9 million; (2) an increase in prepaid and other assets of $27.4 million, which includes land of $23.4 million reclassified from property plant and equipment to asset held for sale within prepaid expense and other assets on our Consolidated Balance Sheet; and (3) an increase in accounts receivable of $22.4 million.
Other Commitments—Revolving Credit Facility On October 20, 2006, we entered into a five-year, $300.0 million senior unsecured revolving credit facility providing for loans to Synopsys and certain of its foreign subsidiaries.
The facility replaces our previous $250.0 million senior unsecured credit facility, which was terminated effective October 20, 2006.
The amount of the facility may be increased by up to an additional $150.0 million through the fourth year of the facility.
The facility contains financial covenants requiring us to maintain a minimum leverage ratio and specified levels of cash, as well as other non-financial covenants.
The facility terminates on October 20, 2011.
Borrowings under the facility bear interest at the greater of the administrative agent’s prime rate or the federal funds rate plus 0.50%; however, we have the option to pay interest based on the outstanding amount at Eurodollar rates plus a spread between 0.50% and 0.70% based on a pricing grid tied to a financial covenant.
In addition, commitment fees are payable on the facility at rates between 0.125% and 0.175% per year based on a pricing grid tied to a financial covenant.
As of October 31, 2006 we had no outstanding borrowings under this credit facility and were in compliance with all the covenants.
We believe that our current cash, cash equivalents, short-term investments, cash generated from operations, and available credit under our credit facility will satisfy our business requirements for at least the next twelve months
We plan to continue to scale the capacity and enhance the capability and reliability of our infrastructure to support user growth and increased activity on our platform.
We also expect that the amount of revenue generated from the sale of our advertising services on third-party publishers’ websites, applications and other offerings will vary.
As a result, we expect that cost of revenue will vary in absolute dollar amounts for the foreseeable future and vary in the near term from period to period as a percentage of revenue.
Research and Development Research and development expenses consist primarily of personnel-related costs, including salaries, benefits and stock-based compensation, for our engineers and other employees engaged in the research and development of our products and services.
In addition, research and development expenses include amortization of acquired intangible assets, allocated facilities and other supporting overhead costs.
## Table 1 ##
2017 Compared to 2016.
In 2017, research and development expenses decreased by $171.5 million compared to 2016.
The decrease was attributable to a $141.6 million decrease in personnel-related costs, mainly driven by a decrease in stock-based compensation expense, a $25.9 million decrease in restructuring charges net of a one-time nonrecurring gain on sale of assets in 2017, a $23.7 million decrease in allocated facilities and other supporting overhead expenses due to a decrease in overall total expenses, a $2.6 million decrease in other expenses, and a $2.5 million decrease in depreciation and amortization expense, offset by a $24.8 million decrease in the capitalization of costs associated with developing software for internal use.2016 Compared to 2015.
In 2016, research and development expenses decreased by $93.2 million compared to 2015.
The decrease was primarily attributable to a $69.1 million decrease in personnel-related costs, mainly driven by a decrease in compensation expense from a decrease in average employee headcount, a $42.7 million increase in the capitalization of costs associated with developing software for internal use due primarily to an increase in the number of projects as we refine our core services, and a $2.5 million decrease in other expenses.
The decreases were offset by a $9.1 million increase in allocated facilities and other supporting overhead expenses, a $7.2 million increase in restructuring expenses and a $4.8 million increase in depreciation expense.
We plan to continue to invest in key areas of our business to ensure that we have the right level of engineering, product management and design teams to support our research and development efforts.
We expect that both research and development headcount and costs in absolute dollars will increase in the near term but will vary from period to period as a percentage of revenue.
Sales and Marketing Sales and marketing expenses consist primarily of personnel-related costs, including salaries, commissions, benefits and stock-based compensation for our employees engaged in sales, sales support, business development and media, marketing, corporate communications and customer service functions.
In addition, marketing and sales-related expenses also include advertising costs, market research, tradeshows, branding, marketing, public relations costs, amortization of acquired intangible assets, as well as allocated facilities and other supporting overhead costs.
## Table 2 ##
?
Future reversal of existing temporary differences ?
Tax-planning strategies ?
Future taxable income exclusive of reversing temporary differences and loss carryforwards As we continue to make significant strides in optimizing operations resulting in improved financial results, our future reassessment is likely to result in the determination that a valuation allowance is no longer required.
This would result in such future financial reporting period in a significant reversal of the valuation allowance and a corresponding material noncash income tax benefit and the recording of additional deferred tax assets on our balance sheet.
Based on recent earnings in certain jurisdictions, sufficient positive evidence may exist within the 2018 calendar year such that we may release a significant portion of our valuation allowance.
Quarterly Results of Operations The following table sets forth our unaudited consolidated statement of operations data for each of the eight quarters in the period ended December 31, 2017.
The unaudited quarterly statement of operations data set forth below have been prepared on a basis consistent with our audited annual consolidated financial statements in this Annual Report on Form 10-K and include, in our opinion, all normal recurring adjustments necessary for a fair statement of the financial information contained in those statements.
Our historical results are not necessarily indicative of the results that may be expected in the future.
The following quarterly financial data should be read in conjunction with our audited consolidated financial statements and the related notes included elsewhere in this Annual Report on Form 10-K.
## Table 3 ##
2018 Compared to 2017.
In 2018, sales and marketing expenses increased by $53.9 million compared to 2017.
The increase was attributable to a $36.2 million net increase in allocated facilities costs and other supporting overhead expenses, a $9.3 million increase in marketing and sales-related expenses, and a $23.9 million net increase in personnelrelated costs driven by an increase in average employee headcount offset in part by a decrease in stock-based compensation expense.
These increases were offset by a $15.5 million decrease in amortization of acquired intangible assets due to certain intangible assets becoming fully amortized.2017 Compared to 2016.
In 2017, sales and marketing expenses decreased by $240.4 million compared to 2016.
The decrease was attributable to a $116.0 million decrease in personnel-related costs, driven by a decrease in average employee headcount mainly as a result of our 2016 restructuring plan, a $54.0 million decrease in marketing and salesrelated expenses, a $28.0 million decrease in allocated facilities and other supporting overhead expenses due to a decrease in overall total expenses, a $27.4 million decrease in restructuring expenses, and a $15.0 million decrease in amortization of acquired intangible assets.
We continue to evaluate key areas in our business to ensure we have the right level of sales and marketing to execute on our key priorities and objectives.
We expect that sales and marketing costs will increase in absolute dollar amounts and vary as a percentage of revenue.
General and Administrative General and administrative expenses consist primarily of personnel-related costs, including salaries, benefits and stock-based compensation, for our executive, finance, legal, information technology, human resources and other administrative employees.
In addition, general and administrative expenses include fees and costs for professional services, including consulting, third-party legal and accounting services and facilities costs and other supporting overhead costs that are not allocated to other departments.

Tables referenced above, in order (Table 0 first):
<table><tr><td>October 31, 2006</td><td>October 31, 2005</td><td>Dollar Change</td><td>% Change</td></tr><tr><td>(dollars in millions)</td><td></td><td></td></tr><tr><td>$122.6</td><td>$100.2</td><td>$22.4</td><td>22%</td></tr></table>
<table><tr><td></td><td colspan="3">Year Ended December 31,</td><td rowspan="2">2016 to 2017 % Change</td><td rowspan="2">2015 to 2016 % Change</td></tr><tr><td></td><td>2017</td><td>2016</td><td>2015</td></tr><tr><td></td><td colspan="3">(in thousands)</td><td></td><td></td></tr><tr><td>Research and development</td><td>$542,010</td><td>$713,482</td><td>$806,648</td><td>-24%</td><td>-12%</td></tr><tr><td>Research and development as a percentage of revenue</td><td>22%</td><td>28%</td><td>36%</td><td></td><td></td></tr></table>
<table><tr><td></td><td colspan="3">Year Ended December 31,</td><td rowspan="2">2016 to 2017 % Change</td><td rowspan="2">2015 to 2016 % Change</td></tr><tr><td></td><td>2017</td><td>2016</td><td>2015</td></tr><tr><td></td><td colspan="3">(in thousands)</td><td></td><td></td></tr><tr><td>Sales and marketing</td><td>$717,419</td><td>$957,829</td><td>$871,491</td><td>-25%</td><td>10%</td></tr><tr><td>Sales and marketing as a percentage of revenue</td><td>29%</td><td>38%</td><td>39%</td><td></td><td></td></tr></table>
<table><tr><td></td><td colspan="8">Three Months Ended</td></tr><tr><td></td><td>Dec. 31, 2017</td><td>Sep. 30, 2017</td><td>Jun. 30, 2017</td><td>Mar. 31, 2017</td><td>Dec. 31, 2016</td><td>Sep. 30, 2016</td><td>Jun. 30, 2016</td><td>Mar. 31, 2016</td></tr><tr><td></td><td colspan="8">(Unaudited, in thousands, except per share data)</td></tr><tr><td>Consolidated Statement of Operations Data:</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Revenue</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Advertising services</td><td>$644,257</td><td>$502,802</td><td>$489,148</td><td>$473,780</td><td>$637,821</td><td>$544,966</td><td>$534,524</td><td>$530,741</td></tr><tr><td>Data licensing and other</td><td>87,303</td><td>86,831</td><td>84,707</td><td>74,471</td><td>79,385</td><td>70,968</td><td>67,434</td><td>63,780</td></tr><tr><td>Total revenue</td><td>731,560</td><td>589,633</td><td>573,855</td><td>548,251</td><td>717,206</td><td>615,934</td><td>601,958</td><td>594,521</td></tr><tr><td>Costs and expenses<sup>-1</sup></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Cost of revenue</td><td>217,979</td><td>210,016</td><td>212,908</td><td>220,339</td><td>305,710</td><td>225,159</td><td>202,966</td><td>198,405</td></tr><tr><td>Research and development</td><td>133,996</td><td>136,115</td><td>143,171</td><td>128,728</td><td>202,128</td><td>177,049</td><td>178,511</td><td>155,794</td></tr><tr><td>Sales and marketing</td><td>189,572</td><td>172,957</td><td>185,296</td><td>169,594</td><td>260,603</td><td>224,436</td><td>236,619</td><td>236,171</td></tr><tr><td>General and administrative</td><td>79,915</td><td>63,266</td><td>70,839</td><td>69,868</td><td>92,392</td><td>67,379</td><td>70,238</td><td>63,267</td></tr><tr><td>Total costs and expenses</td><td>621,462</td><td>582,354</td><td>612,214</td><td>588,529</td><td>860,833</td><td>694,023</td><td>688,334</td><td>653,637</td></tr><tr><td>Income (loss) from operations</td><td>110,098</td><td>7,279</td><td>-38,359</td><td>-40,278</td><td>-143,627</td><td>-78,089</td><td>-86,376</td><td>-59,116</td></tr><tr><td>Interest expense</td><td>-26,700</td><td>-26,732</td><td>-26,396</td><td>-25,409</td><td>-25,281</td><td>-24,860</td><td>-24,934</td><td>-24,893</td></tr><tr><td>Other income (expense), net<sup>(2)</sup></td><td>10,155</td><td>1,922</td><td>-48,320</td><td>7,322</td><td>6,662</td><td>6,640</td><td>6,734</td><td>6,306</td></tr><tr><td>Income (loss) before income taxes</td><td>93,553</td><td>-17,531</td><td>-113,075</td><td>-58,365</td><td>-162,246</td><td>-96,309</td><td>-104,576</td><td>-77,703</td></tr><tr><td>Provision for income taxes</td><td>2,474</td><td>3,564</td><td>3,413</td><td>3,194</td><td>4,808</td><td>6,562</td><td>2,641</td><td>2,028</td></tr><tr><td>Net income (loss)</td><td>$91,079</td><td>$-21,095</td><td>$-116,488</td><td>$-61,559</td><td>$-167,054</td><td>$-102,871</td><td>$-107,217</td><td>$-79,731</td></tr><tr><td>Net income (loss) per share attributable to common stockholders:</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Basic</td><td>$0.12</td><td>$-0.03</td><td>$-0.16</td><td>$-0.09</td><td>$-0.23</td><td>$-0.15</td><td>$-0.15</td><td>$-0.12</td></tr><tr><td>Diluted</td><td>$0.12</td><td>$-0.03</td><td>$-0.16</td><td>$-0.09</td><td>$-0.23</td><td>$-0.15</td><td>$-0.15</td><td>$-0.12</td></tr><tr><td>Other Financial Information:</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Adjusted EBITDA<sup>-3</sup></td><td>$308,174</td><td>$206,999</td><td>$177,874</td><td>$169,939</td><td>$215,107</td><td>$181,316</td><td>$174,602</td><td>$180,468</td></tr><tr><td>Non-GAAP net income<sup>-4</sup></td><td>$141,407</td><td>$77,848</td><td>$56,370</td><td>$53,234</td><td>$77,734</td><td>$61,387</td><td>$59,538</td><td>$65,747</td></tr></table>

Question: As As the chart 3 shows,which year is Total costs and expenses for Three Months Ended Jun. 30 the lowest?
Answer: 2017