The computer has changed the way we work, team, communicate, and play; Virtually ewery kind of organization throughout the world conducts business with computers. Students, teachers, and research scientists use the computer as a learning tool. Millions of individuals and organizations communicate with one another over a network of computers called the Internet. Computer games entertain people of all ages. Almost all computers are electronic digital computers. They are electronic in their use of electric current(电流) to carry information. They are digital in. that they process information as units of electric charge representing numbers. The word digital means having to do with numbers. To enable a computer to process information that is not numerical — such as words, pictures, or sounds — the computer or some other &vice must first digitize: that information. A device digitizes information by translating it into charges that represent numbers. After the computer processes the digitized information by working with the charges, the computer or a device: connected to the computer translates its results hack into their original form. Thus, an artist might use a machine called a scanner to digitize a photograph. The artist would next process the resulting electric charges in a computer to Change the photograph perhaps to add a border. The artist would then use a printer connected to the computer to produce a, copy of the altered photo. Digital computers are one of two general kinds of computers. The other kind is calculating devices called analog computers. An analog computer represents amounts with physical quantities, such as distances along a scale, rather than with numbers. The main topic of this passage is ______.

A. digital computers
B. the future of computer
C. computer science
D. computer and teachers.