问题
单项选择题
（）is not a physical wall but a flow virtual data to protect the computer network.
A.data wall
B.data channel
C.database
D.firewall
答案
参考答案：D
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（）is not a physical wall but a flow virtual data to protect the computer network.
A.data wall
B.data channel
C.database
D.firewall
参考答案：D