Answer:
A clause that may modify a verb is an Adverb Clause.
Step-by-step explanation:
Just as an adverb is a word that modifies a verb, the same would be said for a clause. An adverb clause add information that elaborates where, when, why, how, and how much. While the question says, "may modify", this is because adverbs also modify adjectives and other adverbs.