1. The original price of a commodity is $a$ yuan. During the Spring Festival promotion, it is reduced by $20 \%$. If the price is to be restored to the original price after the festival, the current selling price should be increased by ( ).
(A) $15 \%$
(B) $20 \%$
(C) $25 \%$
(D) $30 \%$
- 1.C.

Let the price increase be $x \%$. According to the problem, the equation is $a(1-20 \%)(1+x \%)=a$. Solving this, we get $x=25$.