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：考查宾语补足语。本句的it指代the traffic rule，与explain构成被动关系，故使用过去分词的形式。句意：到现在为止你应该能理解交通规则，我已经和你解释足够多次了。故D正确。