Which Two Conditions Are Necessary for High Availability to Function

Which two conditions are necessary for high availability to function between two Cisco FTD devices? (Choose two.)

A) The units must be the same version
B) Both devices can be part of a different group that must be in the same domain when configured within the FMC.
C) The units must be different models if they are part of the same series.
D) The units must be configured only for firewall routed mode.
E) The units must be the same model.