You are configuring an 802.1Q trunk between a Layer 2 switch and a firewall. You read in the documentation that the best way to set up a trunk is to set the port as dynamic desirable. The trunk is not coming up. Which one of these options would be a valid explanation？（）

A.The firewall does not support Cisco Discovery Protocol. You should set the switchport trunk mode ON

B.The firewall does not support Cisco Discovery Protocol. You should set the switchport trunk mode to OFF

C.The firewall does not support Cisco Discovery Protocol. You should set the switchport trunk mode as auto

D.The firewall does not support DTP.You should set the switchport trunk mode to ON