This robot is supposed to save a lot of labor, but it remains a problem if it ______.

In North America, most students go to school_____ the school bus.[ ]

What time do you expect me back, Mum?— Say, _____ half an hour. [ ]

It is the first time that you have come to China, _____?

What did the man say to you? —- He ________ me where the post office ________.