长期以来，网络操作系统的3大传统阵营指的是：Microsoft的Windows NT、Novell的NetWare和( )。

A．UNIX

B．Linux

C．OS/2

D．DOS

Anti- virus software protects your computer from viruses by (75) your computer’s memory and disk devices.

A．deleting

B．changing

C．scanning

D．replacing