中国古代存在阶层性差别，上层频繁，下层（）。

A. to prevent unauthorized Telnet access to a switch port
B. to limit the number of Layer 2 broadcasts on a particular switch port
C. to prevent unauthorized hosts from accessing the LAN
D. to protect the IP and MAC address of the switch and associated ports
E. to block unauthorized access to the switch management interfaces over common TCP port

A. 正确
B. 错误