2019年mpa考试英语真题——非谓语动词15

{01}There is no doubt that hiking is good for the retired couple, but it remains ________ whether they will enjoy it
A.to see
B.seeing
C.to be seen
D.seen
解析：
本题选C。

{02}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
解析：
本题选C。