If you can’t understand these sentences, your constant lack of handing in homework ____.

After the whistle rang, the coach appeared in the field. Behind him        the team wearing black and white suits.

— Can you come to my birthday party tonight? — I’d love to, but I______ on a patient at 6 o’clock.

 Just look at the room. My roommate ____ up his clothes.

—Your colleague's spoken English is quite good, Amy．— No wonder, as she              in the USA for two years．