Mr. Wang told us that the moon ______ round the earth.

It’s very difficult to see ____ the window because the glass is very dirty.[ ]

There is somebody knocking at the door. Who________ it be?—I’m not sure. It ________ be a postman.

The Chinese mainland has become the world’s second______ market for iPhone.

My father’s office is at the top. I can see the whole city ______ the office. [ ]