An administrator is creating interface objects to better segment their network but is having trouble adding interfaces to the objects. What is the reason for this failure?
A. The interfaces are being used for NAT for multiple networks
B. The administrator is adding interfaces of multiple types
C. The administrator is adding an interface that is in multiple zones
D. The interfaces belong to multiple interface groups
I would go with B:
All interfaces in an interface object must be of the same type: all inline, passive, switched, routed, or ASA FirePOWER.
https://www.cisco.com/c/en/us/td/docs/security/firepower/620/configuration/guide/fpmc-config-guide-v62/reusable_objects.html#ID-2243-000009b4