Answer: C) could have forgotten.
Explanation: A verb phrase is a syntactic unit consisting of an auxiliary verb preceding the main verb. A verb phrase can be the predicate of a sentence or a clause. In the given sentence: "Could you have forgotten your sunglasses in the car" the verb phrase is formed by the helping verbs "could have" and the main verb "forgot" in its past participle form "forgotten", we don't include "you" because it is the subject of the sentence.