The flu is believed by viruses inside the human nose and throat. [ ]A. causing B
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![The flu is believed by viruses inside the human nose and throat. [ ]A. causing B](/pic/43_1428287.jpg)
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
试题答案
C