C

試題分析：考查固定句型：It will/may be+一段時間+before….過多長時間才/就….句意是：科學家說可能要5到6年這種藥才能在病人身上做實驗。選C。
點評：有的固定句型很相似：有的是時態(tài)的區(qū)別，如果：It is+一段時間+since…,注意辨別清楚。
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