Adverbs refer to the words which modify an adjective, a verb or an adverb. Adverbs further answers to the following question of,
<em>How? Where? When? and Why?</em>
Therefore, in the sentence, <em>yesterday Rachel worked slowly because she was so tired.</em>
Words which function as an adverb are- yesterday, so and slowly.
Yesterday answers from the following questions of<em> when?</em>
So acts as a modifier to an adverb <em>slowly</em>, and
Slowly modifies an adjective <em>slow</em>.
Answer:
She is not writing a letter.
