A、Because they were developed very well. B、Because they were portable for every consumers. C、Because they sold very well in the

(19)The first modern digital computers were developed in the 1940s for military purposes that arose during World War Ⅱ. These computers filled entire rooms, and with rates of a few thousand calculations per second, they took hours to perform complex mathematical operations. In the 1970s, the first personal computers were sold. Fitting on a desktop, they are exponentially faster and more powerful than the computers that had once filled large room. (20)They were also affordable to individual consumers, which made it possible for many people to use them for personal, business and academic needs. By the mid-1990s, laptop computers able of millions of calculations per second had been developed. Currently, nearly half of the American homes have a personal computer, and businesses have come to rely on computers for nearly every function.
Now that computers are small, powerful, cheap, and affect every part of our lives, (21)the next step will be the formation of a network connecting all of these computers to each other. On this network, which some people are calling the information highway, great changes take place every day. The changes to society will be as revolutionary as those of the Industrial Age and the Renaissance. Not only will people shop and conduct business through their computers, but they will also engage with every type of human activity, from reading to simply hanging with friends. Computer networks will bring many benefits in the areas of business, education, and social interaction, producing widespread sharing of knowledge, wealth and the worldwide cultural renewal.
Questions 19 to 21 are based on the passage you have just heard.
19.When were the first modern digital computers developed?
20.Why could many people use personal computers?
21.What’s the next step for computers?