阅读下列短文，从每小题所给的四个选项中选出一个最佳答案。

　　The United States is not the only country affected by the “computer revolution ”. All the major countries of the world have computers, and the developing countries have also realized that computers play a big part in their economic development.

　　Usually what one sees is a machine that looks like a typewriter; it is called a computer terminal (终端). But computers are also used in unseen ways. For example. they determine how much time there should be between traffic signals to prevent traffic problems and to keep millions of cars moving in an orderly flow. When you buy a car, a factory process (过程) that is controlled by a computer enables you to obtain a car with your own choice of colors and special features(特征) in just a few weeks' time. In medical laboratories, computers have reduced the mistakes in testing, and they have saved doctors' countless hours of work. Before long, medical histories of all Americans will be kept in computer “banks”. If a person becomes ill far from his home, local doctors will be able to get his medical record immediately. In science, the computer has performed in minutes experiments which would have required thousands of hours of work by human hands and minds.

　　Most experts agree that computers are necessary to solve the problems of increasing population, city living, and public affairs. Without computers, the jobs of solving these problems would require millions of workers to do tons of paperwork. Before any computer can work on any problem, it must be told what to do. Someone must program the computer, step-by-step. At first this was done by having the programmer write out his instructions in the form of numbers which would be “understood” by the machine. Within a short time, attempts were made to perform a system that would enable humans to communicate more easily with machines. Different “languages” were developed by means of which the programmer could use words that had meanings for him, and another program in the machine would translate the words into the computer's number system.

　　Without special training, it is impossible to understand exactly how a computer does its work. However, many people without scientific training use computers in their daily lives. In some American schools, for example, young children are being taught by computers for part of the school day.

　　The use of computers in school has worried some Americans. There are those who fear it will remove human element (成分) from teacher-student relationships. On the other hand, there are educators who consider computer program a valuable means of freeing teachers from the more boring and tiring tasks, thus enabling them to spend more time with a single student.

　　In education, as in business and industry, science and medicine, computers play an important part in almost every type of operation. The future will bring major advances in computer technology, which will aid man in his efforts to improve the world.

1．According to the context, the author has written the passage mainly for ________ .

[　　]

A．young children

B．experienced operators

C．common readers

D．scientists in the computer field

2．Operators of computers should give instructions to work in the form of program ________ .

[　　]

A．which are introduced in turn into computers

B．through which computers could process “language”

C．which could tell computers what to do and how to do

D．all of the above

3．The arguments for computer program used in education were that

[　　]

A．computers like toys would attract much attention of school children

B．there are lots of buttons which you can press for doing anything at your will

C．computer program would take the place of teachers, turning a school into a computer world

D．computers could give teachers the opportunity to spare time to deal with students respectively

4．Which of the following best express the main idea of this passage?

[　　]

A．The world will enjoy the beautiful picture of the computers.

B．Computer technology will change the human life.

C．Computer would work freely in the future.

D．Computer would work with a great memory-storage and at highest speed.