DTA recognition:decrease in a valuation allowance for a deferred tax asset

Which of the following events will most likely result in a decrease in a valuation allowance for a deferred tax asset under U.S. GAAP? A(n):)A. reduction in tax rates.B. extension in the tax loss carry-forward period.C. decrease in interest rates.

please help, I think valuation allowance has nothing to do with those option. firm could set allowance as much as they want.