题目内容：
What is a "benign" virus?
A．It is a virus that causes great damage. B．It is a virus that once infected the IBM's computer system.
C．It is a virus that carries a Christmas greeting.
D．It is a virus that causes no harm to the computer systems.
参考答案：【答案仅供学习，请勿对照自行用药等】
答案解析：