The children not to play football in the street.A. warnB. warnedC. must warnD. are warned

问题补充：

The children not to play football in the street.

A. warn

B. warned

C. must warn

D. are warned

答案：

A. warn

B. warned

C. must warn

(答案→)D. are warned

解析：这是被动语态, be warned not to do,意思是: 警告某人不要做……