As we all know it’s not polite to keep others for a long time.A. waitB. waitedC. to wait

问题补充：

As we all know, it’s not polite to keep others for a long time.

A. wait

B. waited

C. to wait

D. waiting

答案：

A. wait

B. waited

C. to wait

(答案→)D. waiting

解析：这里考核keep doing sth和keep sb doing sth结构。

注意：others这里是“别人”的意思。