At one time it was as large as a room, and quite difficult and slow to operate. But, since the invention of the silicon ship, which is really a very very small electric circuit, computers have been greatly improved. They have become smaller, easier to use, and faster; they can store a lot more information.

　　Some computer are made as well as television sets. Simple computers can be made smaller than a book. And computers are getting smaller all the time.

　　There are several reasons why the computer is useful to us. Firstly, it can store a very very large quantity of information in its memory. Secondly, the computer can operate very quickly thousands of times faster than a humanand it will not tire. Thirdly, modern computers can be built into other kinds of machines, like radios, cars, planes and so on. They can do many kinds of work.

　　Soon, almost everyone, either at home or at work, will use some kind of computer. the lives of all of us will be changed by this invention.

　　The main idea of this passage is ____

　　A how the computer came into being

　　B that computers ate getting smaller and smaller all the time

　　C that the computer will change the lives of all of us

　　D that modern computers can be built into other machine