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精英家教網 > 高中英語 > 題目詳情

Scientists say it may be five or six years ____ it is possible to test this medicine on human patients.

       A.since B.after  C.before      D.when      

C


解析:

此題考查連詞以及對句式的理解。It is + 一段時間+before,意為“要(多長時間)……才能……”。

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