◎ 题干
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
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“You should understand the traffic rule by now. You've had it often enough.[ ]A. explainingB. to explain C. explainD. explained…”主要考查了你对  【过去分词】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。