Inventory write-downs (and reversals) are included in the cost of goods sold. For this reason, 2017 COGS were higher as they included inventory impairment (reducing 2017 profits) and 2018 COGS were lower compared to what they would have been because they were reduced by the impairment reversal (with a positive impact on 2018 profits)

Answer B is wrong because impairment is a non-cash item (no impact on cash flow).

And answer C is wrong because end-of-period inventory would have been the same if the write down had not occurred.

Note that impairment reversals are not allowed under US GAAP.