Scientists say it may be five or six years _______ it is possible to test this medicine on human pat...
2023-01-21 20:44:16 60次 2014届浙江省温州市高一第一次月考英语题 单项填空 反馈错误 加入收藏 正确率 : 100%
题目内容：
Scientists
say it may be five or six years _______ it is possible to test this medicine on
human patients.
A.
since B. after
C. before D. when
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