请解释下valuation allowance？

问题如下：

An analyst is reviewing a company with a large deferred tax asset on its balance sheet. She has determined that the firm has had cumulative losses for the last three years and has a large amount of inventory that can only be sold at sharply reduced prices. Which of the following adjustments should the analyst make to account for the deferred tax assets?

选项：

A.Record a deferred tax liability to offset the effect of the deferred tax asset on the firm's balance sheet.

B.Recognize a valuation allowance to reflect the fact that the deferred tax asset is unlikely to be realized.

C.Do nothing. The difference between taxable and pretax income that caused the deferred tax asset is likely to reverse in the future.

解释：

A valuation allowance is used to offset deferred tax assets if it is unlikely that those assets will be realized. Because the company has a history of losses and inventory that is unlikely to generate future profits, it is unlikely the company will realize its deferred tax assets in full.