单项选择题
The virus can affect the computers in the computer system by （）
A．turning off the power B．making them copy itself C．sending them copies of itself D．sending them some destructive ordens directly
单项选择题 In paragraph 1, "They were linked by telephones", "they" refers to （）
单项选择题 Which of the following statements is true（）
单项选择题 A computer virus （）
