机库的飞机停放和维修区，通常设有悬挂机坞和地面机坞，以满足不同的飞机维修要求。下列不属于悬挂机坞的是（）。

A．机头坞 

B．机身坞 

C．机翼坞 

D．机尾坞

I think Tom, as the head of a big department, should cither study regularly or______his job. [ ]

A. quits

B. to quit

C. quitting

D. quit