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

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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