A.If a bit is turned on (1), the corresponding bit in the IP address is used for the host portion.
B.If a bit is turned off (0), the corresponding bit in the IP address is used for the host portion.
C.If a bit is turned on (1), the corresponding bit in the IP address is used for the network prefix.
D.If a bit is turned off (0), the corresponding bit in the IP address is used for the network prefix.
参考答案：BC
