问题补充:
Scientists say it may be five or six years it is possible to test this medicine to human patients.
A. since
B. after
C. before
D. when
答案:
A. since
B. after
(答案→)C. before
D. when
解析:考查固定句型:It will be/may be+一段时间+before表示要过多长时间才做某事,由此题看是填before,意思是:科学家说要过五年或十年才能在人身上试验这药.选C。