The environment is becoming worse and worse. I think we should do something to ____ people ____ cutting the trees in order to protect the earth.
The red suitcase is expensive ______it’s made of leather.
Could you show me how to ________ this new recorder?
Some people think that CD-ROMs will soon be _________ books.
I didn’t _____ you were going to leave_____ 3 o’clock.
A human ______ can do some things better than a computer, for example, creating new ideas.