The flu is believed________ by viruses that like to reproduce in the cells inside the human nose and throat．

1. A.
   causing
2. B.
   being caused
3. C.
   to be caused
4. D.
   to have caused

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

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.to have caused

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?

The flu is believed ______ by viruses that like to reproduce in the cells inside the human nose and throat.

A. to be caused                   B. to have caused               C. being caused                   D. causing