What is the purpose of the switchport command?

What is the purpose of the switchport command?
Switch(config-if)# switchport port-security maximum 1
Switch(config-if)# switchport port-security mac-address 0018.DE8B.4BF8

A.
It ensures that only the device with the MAC address 0018.DE8B.4BF8 will be able to connect
to the port that is being configured.

B.
It informs the switch that traffic destined for MAC address 0018.DE8B.4BF8 should only be sent
to the port that is being configured.

C.
It will act like an access list and the port will filter packets that have a source or destination
MAC of 0018.DE8B.4BF8.

D.
The switch will shut down the port of any traffic with source MAC address of 0018.DE8B.4BF8.