It’s four o’clock in the afternoon. The boys in the pool.A. is swiming B. are swimingC. a

问题补充：

It’s four o’clock in the afternoon. The boys in the pool.

A. is swiming

B. are swiming

C. are swimming

D. is swimming

答案：

A. is swiming

B. are swiming

(答案→)C. are swimming

D. is swimming

解析：根据前文的内容. It’s four o’clock in the afternoon，可知答案为C，表示现在进行时。