问题描述：
-How long did the meeting last this afternoon?
- How long did the meeting last this afternoon
- It was supper time ______the meeting was over.
答案是when 为什么at which不行?
- How long did the meeting last this afternoon
- It was supper time ______the meeting was over.
答案是when 为什么at which不行?
问题解答：
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