He had just sent an email to his pal on the Internet ________ the system broke down. A．while B．when...
2022-12-06 16:12:23 85次 2013-2014学年山西省高二8月月考英语试卷（解析版） 单项填空 反馈错误 加入收藏 正确率 : 100%
题目内容：
He had just sent an email to his pal on the Internet
________ the system broke down.
A．while B．when
C．after D．since
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