◎ 题干
The flu is believed _____ by viruses that like to reproduce in the cells inside the human nose and throat.    
[     ]
A. causing                      
B. being caused    
C. to be caused                  
D. to have caused
◎ 答案
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“The flu is believed _____by viruses that like to reproduce in the cells inside the human nose and throat. [ ]A. causingB. being caused C. to be causedD. to …”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。