Question

Which sentence uses the comparative form of an adverb?

A.
Christine ran slower than her sister.

B.
Polly sometimes eats dinner early.

C.
The wind blew fiercely through the trees.

D.
We finished the zoo tour most rapidly.

Answer 1

A. Christine ran slower than her sister. 
Slower  is comparing Christine's speed to the speed of her sister.

Answer 2

the answer is A. 
Christine ran slower than her sister.