单项选择题
在下面的配置中，哪个命令是其他命令得以生效的前提条件
S3#
config t
S(config)#
int fa0/3
S3(config-if#
switchport port-security
S3(config-if#
switchport port-security maximum 3
S3(config-if#
switchport port-security violation restrict
S3(config-if#
Switchport mode-security aging time 10
A．switchport mode-security aging time 10
B．switchport port-security
C．switchport port-security maximum 3
D．switchport port-security violation restrict