问题描述：
英语 过去完成时 until
I did not understand the problem until he had explained it.
过去完成时表示两个动作中较早的过去.这个句子中,明明是先不懂、再解释,为什么had放在解释那边?
I did not understand the problem until he had explained it.
过去完成时表示两个动作中较早的过去.这个句子中,明明是先不懂、再解释,为什么had放在解释那边?
问题解答：
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