4. Discontinued Operations
In fiscal 2019, we sold our Subsea Communications (“SubCom”) business for net cash proceeds of $297 million and incurred a pre-tax loss on sale of $86 million, related primarily to the recognition of cumulative translation adjustment losses of $67 million and the guarantee liabilities discussed below. The definitive agreement provided that, if the purchaser sells the business within two years of the closing date, we will be entitled to 20% of the net proceeds of that future sale, as defined in the agreement, in excess of $325 million. The sale of the SubCom business, which was previously included in our Communications Solutions segment, represents our exit from the telecommunications market and was significant to our sales and profitability, both to the Communications Solutions segment and to the consolidated company. We concluded that the divestiture was a strategic shift that had a major effect on our operations and financial results. As a result, the SubCom business met the held for sale and discontinued operations criteria and has been reported as such in all periods presented on our Consolidated Financial Statements.
Upon entering into the definitive agreement, which we consider a level 2 observable input in the fair value hierarchy, we assessed the carrying value of the SubCom business and determined that it was in excess of its fair value. In fiscal 2018, we recorded a pre-tax impairment charge of $19 million, which was included in income (loss) from discontinued operations on the Consolidated Statement of Operations, to write the carrying value of the business down to its estimated fair value less costs to sell.
In connection with the sale, we contractually agreed to continue to honor performance guarantees and letters of credit related to the SubCom business’ projects that existed as of the date of sale. These guarantees had a combined value of approximately $1.55 billion as of fiscal year end 2019 and are expected to expire at various dates through fiscal 2025; however, the majority are expected to expire by fiscal year end 2020. At the time of sale, we determined that the fair value of these guarantees was $12 million, which we recognized by a charge to pre-tax loss on sale. Also, under the terms of the definitive agreement, we are required to issue up to $300 million of new performance guarantees, subject to certain limitations, for projects entered into by the SubCom business following the sale for a period of up to three years. At fiscal year end 2019, there were no such new performance guarantees outstanding. We have contractual recourse against the SubCom business if we are required to perform on any SubCom guarantees; however, based on historical experience, we do not anticipate having to perform.
The following table presents the summarized components of income (loss) from discontinued operations, net of income taxes, for the SubCom business and prior divestitures:
(1) Included a $19 million impairment charge recorded in connection with the sale of our SubCom business.
(2) Included a $19 million credit related to the SubCom business’ curtailment of a postretirement benefit plan.
Table:
 |  | Fiscal | 
 | 2019 | 2018 | 2017
 |  | (in millions) | 
Net sales | $  41 | $  702 | $  928
Cost of sales | 50 | 602 | 653
Gross margin | (9) | 100 | 275
Selling, general, and administrative expenses | 11 | 48 | 50
Research, development, and engineering expenses | 3 | 39 | 40
Restructuring and other charges (credits), net | 3 | 30 (1) | (3)
Operating income (loss) | (26) | (17) | 188
Non-operating income, net | — | — | 22 (2)
Pre-tax income (loss) from discontinued operations | (26) | (17) | 210
Pre-tax gain (loss) on sale of discontinued operations | (86) | (2) | 3
Income tax (expense) benefit | 10 | — | (70)
Income (loss) from discontinued operations, net of income taxes | $  (102) | $  (19) | $  143


Question: In which year was the amount of Cost of sales largest?
Answer: 2017
Calculation: 653>602>50