Which is likely to cause standard failover via the special serial cable not to work? Choose two.

A.
The two PIX Firewalls are running different versions of software.

B.
The secondary PIX Firewall has not been properly configured as a secondary PIX Firewall.

C.
The hardware models are different.

D.
The standby PIX Firewall has not yet replicated its configuration to the primary PIX Firewall.

E.
The hardware models are the same.

F.
The secondary PIX Firewall has a 3DES license.