scores of times but he still couldn’t understand it ．A. Having explainedB. Having been

问题补充：

scores of times , but he still couldn’t understand it ．

A. Having explained

B. Having been explained

C. Though it was explained

D. It was explained

答案：

A. Having explained

B. Having been explained

C. Though it was explained

(答案→)D. It was explained

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