Which describes the structure of this sentence?

If the ball needs air, use the pump in the storage room.

A.

compound-complex

B.

simple

C.

complex

D.

compound

This sentence is a complex sentence. Usually, a complex sentence is composed of one independent clause and one or more dependent clause. In the sentence, there is one independent clause (use the pump in the storage room) and one dependent clause (if the ball needs air). So, the answer is C.