C) completely
As I am sure you know, adverbs are basically “helping” words that “add” to the understanding and/or imagery of a verb. (One thing to look out for, too, is the suffix “ly” because “ly” is the suffix (ending) that an adverb will typically have though it is important to remember that this will not absolutely be always the case.) That said, let’s first look at the word with the “ly”—“completely.” At this point, we must ask ourselves whether or not completely” adds to the an action word. Completely what? Completely answered. Thus, we have a better understanding of how things were answered—completely. Though, however, there is another verb in the sentence—“leaving”—there is not a word that helps or adds to it.