C. because that is what you are talking about and describing.A word, phrase,clause that functions as an adjective or adverb to provide additional information about another word or word group.
For example:
Donny is an energetic person.
You are describing Donny.
In order to answer your question think about who or what is being described and that is your answer.
This is partially from a web.
Hope this helps :0)
