The rivers will become dirtier and dirtier ______ we take action to protect them. A. since B. if C. ...
2023-01-05 06:19:54 110次 2014-2015学年安徽铜陵县第三中学九年级下开学考试英语试卷（解析版） 单项填空 反馈错误 加入收藏 正确率 : 100%
题目内容：
The rivers will become dirtier and dirtier ______ we take action to protect them.
A. since B. if
C. until D. unless
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