Eric is not going to Nanjing by ______ plane．Instead，he is taking ______ train．（　　）

A．/， aB．a， /C．a， theD．the， a

We finished the rest of the dinner ______ silence after we heard what he told us．（　　）

A．onB．atC．inD．of

Mum，_____ I go out to watch a movie？

Yes，you can．But you must finish your homework first．（　　）

A．mustB．needC．willD．may

What were Helen and Sally doing when it began to rain heavily？

Helen was sleeping _______Sally was reading a magazine．（　　）

A．whileB．untilC．beforeD．after

Is this photo taken in Tibet？

Yes，you can see beautiful snow mountains in the _______of the photo．（　　）

A．expressionB．background

C．introductionD．shape