Answer:
The word <em>not</em> modifies the word <em>exactly.</em>
Explanation:
An abverb is a word (or phrase) that modifies a verb (or adjective, or even another adverb). When modifying a verb, an adverb basically says <em>how </em>something is done.
Adverbs often end in -ly. We can spot the word <em>exactly, </em>which is describing the action of having something in mind. The word <em>not,</em> which is also an adverb, modifies the word <em>exactly</em> because it changes something about the meaning of <em>exactly.</em>