Which requirement for the FTD high availability setup is true?

Which requirement for the FTD high availability setup is true?
A . Units must be in different domains in FMC
B . Units must have DHCP configured for the interfaces
C . Units must not have the same major, minor, and maintenance software version running on them
D . Units can have any uncommitted changes on FMC and need not be fully deployed
E . Units must be synchronized using the same NTP source.
F . Units must be configured in routed mode
G . Units must be configured in transparent mode

Answer: E