The cause of this kind of flu hasn’t yet______in spite of the efforts of the medical researchers.

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问题 The cause of this kind of flu hasn’t yet______in spite of the efforts of the medical researchers.

选项 A、have discovered
B、discovered
C、been discovered
D、discover

答案C

解析 现在完成时+被动语态。
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本试题收录于: 英语题库普高专升本分类
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