问题
选择题
Scientists say it may be five years _____ it is possible to test this medicine on human patients.[ ]
A. since
B. until
C. before
D. when
答案
答案：C
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Scientists say it may be five years _____ it is possible to test this medicine on human patients.[ ]
A. since
B. until
C. before
D. when
答案：C