The flu is believed by viruses that like to reproduce in the cell inside the human nose and throat.
A. causing
B. being caused
C. to be caused
D. to have caused
网友回答
A. causing
B. being caused
(答案→)C. to be caused
D. to have caused
解析: 在“sb/sth is/was+过去分词+不定式”句型中,如果不定式所表示的动作在谓语动词后面发生,动词不定式要用一般式。