◎ 题干
The flu is believed _____ by viruses inside the human nose and throat.

A. causing
B. being caused
C. to be caused
D. be have caused
◎ 答案
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◎ 解析
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◎ 知识点
    根据魔方格专家分析,试题“The flu is believed _____by viruses inside the human nose and throat.[ ]A. causing B. being caused C. to be caused D. be have caused …”主要考查了你对  【不定式的被动式】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。