Which is a complete sentence?

a. The sound of thunder.

b. When Monica went to the dentist.

c. Loud noises disturbed the neighbors.

d. Treated him to a new video game.

C. Loud noises disturbed the neighbors.

Among the choices given above, only this sentence expresses a complete thought. A sentence is defined as words meaningfully grouped to express a complete thought. Most of the time, it has a subject and a predicate. In this sentence, the complete subject is ‘loud noises’ and the complete predicate is ‘disturbed the neighbors’. Basically, the sentence conveys the meaning that the neighbors are disturbed by loud noises. All the other choices are phrases or sentence fragments.