[单项选择]The computer is fast, and seldom makes a mistake, while people are too slow, and full of mistakes sometimes. That is what people often say about computers. For over a quarter of a century engineers have been making better and better computers. Now a computer can do a lot of everyday jobs wonderfully. It is widely used in factories, hospitals, banks and universities. A computer can report, decide and control in almost every field. Many computer scientists are now thinking of making the computer "think" like a man. With the help of a person, a computer can draw pictures, write music, talk with people, play chess, recognize voices, translate languages, and so on. Perhaps computers will one day really think and feel. Do you think the people will be afraid when they find that the computer is too clever to listen to and serve the people

Engineers have worked on computers for ______.
A. about a whole century
B. more than twenty-five years
C. over three months