18. In the following sentence, which word is an adverb used to modify a verb?

The young girl quickly learned the rules of the board game.

[A. Quickly]
B. Girl
C. Game
D. Learned
is my answer correct

Right.

People express thoughts mainly by using

people express thoughts by using lanaguage

Yes, your answer is correct. The adverb in the sentence that modifies the verb "learned" is "quickly." If you need further confirmation or explanation, I can provide it.