Many in the credit industry expect that credit cards will eventually ____ paper money foralmost everypurchase.[ ]

Young kids shouldn’t goswimming alone.—__________.It’s too dangerous.

Listen ! Helen is singing in the next room.It ____ be Helen. She has gone to Beijing.

Farmers have turned to _____deer because it can make a lot of money.

The director couldn’t figure out _______ made his assistant spend so much time in doing the survey. [ ]