Most people think that English is _____ useful language, but some students think it's _____ unimportant subject. [ ]

A. a, an

B. a, an

C. an, an

D. an, a

整车气密性对于车辆的重要性包括：（）

A.保持车内干净减少灰尘进入

B.减少风噪传递到车内

C.减少路噪传递到车内

D.减少动力传动噪音传递到车内

E.影响空调制冷和制热性能