He seldom stays up late at night, ______ necessary, to keep himself full of energy the next day. A.i...
2022-07-03 02:07:21 150次 江苏省2019-2020学年九年级下学期线上教学调研英语试卷 单选题 反馈错误 加入收藏 正确率 : 100%
题目内容：
He seldom stays up late at night, ______ necessary, to keep himself full of energy the next day.
A.if B.unless C.until D.while
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