The children a P.E. class on the playground when it began to rain suddenly.A. haveB. are

问题补充：

The children a P.E. class on the playground when it began to rain suddenly.

A. have

B. are having

C. had

D. were having

答案：

A. have

B. are having

C. had

(答案→)D. were having

解析：句意：但开始下雨时孩子们正在操场上上体育课。当一个动作发生时，另一个动作正在发生，该动作用进行时态，根据句意，故用过去进行时，故选D。