河南成教 / 大学英语（3）
正确率：100%
2[单选题]
Scientists say it may be five or ten years _ _ _ _ _ _ _ it is possible to test this medicine on human patients.
A.since
B.before
C.after
D.when
Scientists say it may be five or ten years _ _ _ _ _ _ _ it is possible to test this medicine on human patients.
参考答案：
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