Scientists say it may be five or six years it is possible to test this medicine
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Scientists say it may be five or sixyears __________it is possible to test this medicine on human patients.
A. since B.after
C. before D. when
试题答案
答案：C
解析：| “It be+一段时间+before…”是固定结构，该结构的意思是“要过……（长）时间才……”。
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