John speaks Chinese fluently because he used to live in China for ten years.    

A Suppose John has lived in China for ten years, he can speak Chinese fluently.

B  Provided that John lived in China for ten years, he could speak Chinese fluently.

C Unless John had lived in China for ten years, he could not have spoken Chinese fluently.

D John could not speak Chinese fluently if he had not lived in China for ten years.