What is a result of enabling Cisco FTD clustering? 

Answer options:

A. For the dynamic routing feature, if the master unit fails, the newly elected master unit maintains all existing connections.
B. Integrated Routing and Bridging is supported on the master unit.
C. Site-to-site VPN functionality is limited to the master unit, and all VPN connections are dropped if the master unit fails.
D. All Firepower appliances support Cisco FTD clustering.

C

Reference: https://www.cisco.com/c/en/us/td/docs/security/firepower/640/configuration/guide/fpmc-config-guide-v64/ clustering_for_the_firepower_threat_defense.html