问题
选择题
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
答案
C
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。