You should understand the traffic rule by now.You’ve had it often enough.A. explainingB.

问题补充：

You should understand the traffic rule by now.You’ve had it often enough.

A. explaining

B. to explain

C. explain

D. explained

答案：

A. explaining

B. to explain

C. explain

(答案→)D. explained

解析：

此题考查“have sth.done”结构。