The black hat is sale. You can buy one only two dollars.[ ]

How long does it take to get to the airport?—Forty minutes. But it’s foggy today. I’m not sure the highway will closes soon. Let’s set off earlier.

This is ______ book I’ve told you about. It’s written by ______ university teacher.

One day， _____，Newton saw an apple fall from a tree.

Carl, why not go and help your sister water the flowers there? —Why__________? I’m busy myself. Jack is lying on the grass doing nothing.