根据短文理解，选择正确答案。
Johnny Smith was a good math student at a high school. He loved his computer. He came home early every day, then he worked with it till midnight. But Johnny was not a good English student, not good at all. He got an F in his English class. One day after school Johnny joined his computer to the computer in his high school office. The school office computer had the grades of all the students: the math grades, the science grades, the grades in arts and music, and the grades in English. He found his English grade. An F! Johnny changed his English grade from an F to A. Johnny' parents looked at his report card. They were very happy.
"An A in English!" said Johnny's Dad. "You're a very clever boy, Johnny."
Johnny is a hacker (黑客). Hackers know how to take informationfrom other computers and put new information in. Using a modem, they join their computers to other computers secretly. School headmasters and teachers are worried about hackers. So are the police, for some people even take money from bank computer accountand put it into their own ones. And they never have to leave home to do it! They are called hackers.
