By the end of this century, the scientists (discover) ______ a cure for the disease.

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问题 By the end of this century, the scientists (discover) ______ a cure for the disease.

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答案will have discovered

解析 本题考查的是动词时态变化。“by the end of”意为“到……时候为止”,所以在出现"by the end of"的句子中,句子时态应是完成时态,通常是过去完成时或将来完成时。本句表示到将来某一时间为止的动作,所以要用将来完成时。试比较:By the end of last week,I had learnt 5000 words. (到上周为止,我已经学了5000个单词。)
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