Correct: B
The question says that the firewall was installed on a "trunk" link between to core switches. This mean Layer-3 is not usable in this situation.
"Virtual wire interfaces by default allow all untagged traffic. You can, however, use a virtual wire to connect two interfaces and configure either interface to block or allow traffic based on the virtual LAN (VLAN) tags. VLAN tag 0 indicates untagged traffic.
You can also create multiple subinterfaces, add them into different zones, and then classify traffic according to a VLAN tag or a combination of a VLAN tag with IP classifiers (address, range, or subnet) to apply granular policy control for specific VLAN tags or for VLAN tags from a specific source IP address, range, or subnet."
https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-admin/networking/configure-interfaces/virtual-wire-interfaces/vlan-tagged-traffic.html