问题描述：
8.Someone called me up in the middle of the night,but they hung up ________I could answer the
8.Someone called me up in the middle of the night,but they hung up _before_I could answer the phone.
有人在半夜给我打电话,但是还没等我接起电话前就挂掉了
这里为什么要用到could 何意
8.Someone called me up in the middle of the night,but they hung up _before_I could answer the phone.
有人在半夜给我打电话,但是还没等我接起电话前就挂掉了
这里为什么要用到could 何意
问题解答：
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