Why is it recommended that you do not use VLAN 1?

A. It is not a production VLAN.
B. It cannot be routed via an SVI.
C. It cannot participate in VTP transfers.
D. It shouldn’t be used for security reasons.

D. For security concerns, it should not be used in production. It is the default VLAN configured on all switches. Potentially, a computer can be plugged into an interface defaulted to VLAN 1 and expose resources such as the switch management network.