Contains a main clause, a subject and an action or linking verb, and makes sense on its own.

Asentence
Bdependent clause
Csubordinating clause
Dcoordinating conjunction

Verified Answer :

b and c per definition don't contain a main clause- so they're wrong answers. d - coordinating conjunction isĀ  just one word, so it does not contain all the things listed above. The correct answer is a). sentence.