Answer:
C) Everyone needs to take his or her test in complete silence.
Step-by-step explanation:
An adverbial phrase is a group of words (two or more) that function as an adverb within a sentence. An adverbial phrase can modify verbs, adjectives or other adverbs in the same way that adverbs do. Moreover, just like adverbs, adverbial phrases respond to the question of how, why, where or when something was done. In this example, the phrase "in complete silence" describes HOW TO TAKE the test.