Which best describes a clause?

Which best describes a clause?Select one of the options below as your answer: A. a word or group of words that should help to describe or make clear the meaning of the word it modifies B. a word that modifies a verb, an adjective, or another adverb C. a group of words that contains a subject and a verb and that is used as part of a sentence D. a group of words that does not contain a verb or a subject and that acts as a single part of speech