问题描述：
He didn't go to sleep ______he finished his homework.C. a
He didn't go to sleep ______he finished his homework.
A. till B. before C. after D. until 选什么,为什么,有什么区别?
He didn't go to sleep ______he finished his homework.
A. till B. before C. after D. until 选什么,为什么,有什么区别?
问题解答：
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