单项选择题

The ______ in e-mail messages has affected almost every computer around the world and has caused the damage of up to US$1 billion in North America.

A．illness
B．virus
C．weakness
D．attachment
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单项选择题
The usual address for a Web site is the ______ page address， although you can enter the address of any page and have that page sent to you.
A．home
B．main
C．host
D．house
单项选择题
Most ______ measures involve data encryption and password.
A．security
B．hardware
C．display
D．program
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