Ladies and gentlemen, please fasten your seat belt. The plane ______.

[      ]

A. takes off

B. is taking off

C. has taken off

D. took off

大批大量生产，装配精度很高，组成件只有2～3个的场合，适宜采用的装配方法是 ( )

A．互换装配法
B．分组装配法
C．修配装配法
D．调整装配法