Where is Mother–She is in the kitchen. She ______ the housework all morning.

31. Do you know when did the world _____?

_______ busy schoolwork, the children also have to take arts, music and sports classes in their free time.-I wonder what they will become.[ ]

What ____ have happened to Kevin? — He might have run into some trouble.

Having __________ no-meat day would be a good way ofencouraging ___________ low carbon life-style.