2. 外语
  3. Scientists say it may be five or six years______this medicine is tested on human beings.

Scientists say it may be five or six years______this medicine is tested on human beings.

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问题 Scientists say it may be five or six years______this medicine is tested on human beings.
选项 A、since
B、before
C、after
D、when
答案B
解析 考察时间状语的连接词，根据题意是说“科学家们说大概要等5到6年，这种药才会在人类身上试验。”before引导时间状语从句，表示“在…之前”。
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