With regard to defense-in-depth, which of the following statements about network design principles is correct?

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With regard to defense-in-depth, which of the following statements about network design principles is correct?

A. A secure network design requires that systems that have access to the Internet should not be accessible from the Internet and that systems accessible from the Internet should not have access to the Internet.
B. A secure network design requires that networks utilize VLAN (Virtual LAN) implementations to insure that private and semi-public systems are unable to reach each other without going through a firewall.
C. A secure network design will seek to provide an effective administrative structure by providing a single choke-point for the network from which all security controls and restrictions will be enforced.
D. A secure network design will seek to separate resources by providing a security boundary between systems that have different network security requirements.