摘要： Bird flu, a contagious disease of animals, is believed by viruses that normally infect only birds and less commonly pigs, and rarely humans. A. caused B. being caused C. to be caused D. to have caused
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Bird flu , a contagious disease of animals , is believed ____ by viruses that normally infect only birds and less commonly pigs , and rarely humans .
A．caused B．being caused C．to be caused D．to have caused
查看习题详情和答案>>Bird flu, a contagious disease of animals, is believed ________ by viruses that normally infect only birds and less commonly pigs, and rarely humans．
- A.caused
- B.being caused
- C.to be caused
- D.to have caused