Put it down, Amy. You mustn’t read letter.

38Donkeys and camels are still widely used in some parts of the world _____ of burden

As a ______, he tries to give the firsthand information of the missing plane to the public as soon as possible.

If ____ mobile phones in class, you will have to be punished according to the school rules.[ ]

It is ___________ the customers’ needs that has made chain stores so popular in big cities in China.