What is the function of the command switchport trunk native vlan 999 on a switch？（）

• A、It designates VLAN 999 for untagged traffic.
• B、It blocks VLAN 999 traffic from passing on the trunk.
• C、It creates a VLAN 999 interface.
• D、It designates VLAN 999 as the default for all unkown tagged traffic.