问题补充:
Scientists say it may be five or six yearsit is possible to test this medicine on human patients.
A. when
B. after
C. before
D. since
答案:
A. when
B. after
(答案→)C. before
D. since
解析:考查固定句型:It will/may be+一段时间+before….过多长时间才/就….句意是:科学家说可能要5到6年这种药才能在病人身上做实验。选C。