在肺周围性结节的诊治中发挥着重要作用的方法

A．神经纤维瘤
B．胸腺瘤
C．畸胎瘤
D．淋巴肉瘤
E．胸骨后甲状腺肿

We must do something to _____ the factories sending out   poisonous gases so as to keep the

city_____.      [ ]

A. keep; being polluted      

B. keep; from being polluted    

C. prevent; being polluted      

D. prevent; from being polluted