[单选题]The flu is believed ________ by viruses that like to reproduce in the cells inside the human nose and throat.
Acause
Bbeing caused
Cto be caused
Dto have caused
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参考答案
试题答案：
C
答案解释：
因为be believed /thought /supposed /said /reported等后要接动词不定式，排除A和B；又因为the flu与cause是被动关系，所以要用不定式的被动式。The flu is believed to be caused by...=It is believed /People believe that the flu is caused by...
