Scientists say it will be five or six years _____ it is possible to test this medicine on human pati...
2023-01-23 08:34:33 60次 2013届北京市高二3月检测练习英语试题 单项填空 反馈错误 加入收藏 正确率 : 100%
题目内容：
Scientists say it will be five or six years
_____ it is possible to test this medicine on human patients.
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A．before
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B．that
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C．since
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D．when
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