A hacker can be dangerous because

A hacker can be dangerous because

A.he knows how to make free long-distance telephone calls

B.vital information is stored in computers. and a hacker knows how to change or erase the information

C.once in jail. he can use a telephone to operate his computer

D.a hacker who steals a free airplane ticket might deprive a doctor of that seat on the airplane

正确答案是B