Which Cisco NAC Appliance component is optional?

A.
NAC Appliance Manager

B.
NAC Appliance Server

C.
NAC Appliance Agent

D.
NAC Appliance Policy Updates

Explanation:
https://www.cisco.com/c/en/us/support/docs/security/nac-appliance-clean-access/112168- nac-oob-acls-00.html#sol-comp
“The Cisco NAC Agent is an optional component of the Cisco NAC solution.”