Question

What is the adverb... my mother's birthday is nearly here.

Answer 1

First, an adverb is a word or phrase that modifies an adjective or verb, telling where, when, how, etc.
So for "My mother's birthday is nearly here.", the adverb would be "nearly" because her birthday is NEARLY here- this modifies "here", which without "nearly", would be just plain "here," which would modify the meaning, wouldn't it? :)