-Has Sam finished his homework today, Anne?

-I have no idea. But he ________ it this morning.[ ]

A．did  

B．had done

C．was doing  

D．had done

“大陆桥”是最典型的______运输。

A．陆海集装箱

B．铁路运输

C．陆路集装箱运输

D．国际铁路集装箱