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. be have caused
网友回答
A. causing
B. being caused
(答案→)C. to be caused
D. be have caused
解析：此题考查非谓语结构。在英语中表示“据说/传/知道……” 的句型是It is said/reported/known that sb./sth.=Sb./Sth. is said/reported/known to...；流感是被引起的，所以选C项。