In which one of these sentences does an adverb modify a verb?

A. Lucy quickly hid behind the tree.

B. Mr. Dodge moved in an extremely slow manner.

C. Jacob was a very smart boy.

D. The dress was terribly old

First, I'm going to highlight all the adverbs in the options:

A. Lucy quickly hid behind the tree.

B. Mr. Dodge moved in an extremely slow manner.

C. Jacob was a very smart boy.

D. The dress was terribly old

Adverbs can modify verbs or adjectives, and in options B, C and D it is adjectives that are modified: slow, smart, old.

The correct answer is A: in option A the adverb modifies a verb