Which statement about N+1 backup is correct?

Which statement about N+1 backup is correct?
A . The model and software version of the active and standby ACs must be exactly the same
B . The main and standby AC product forms can be different, only need to ensure that the AC software version is consistent
C . One backup AC can provide backup services for multiple main ACs, reducing the cost of purchasing equipment, and the reliability is higher than VRRP hot backup
D . N+1 backup is cold backup. AP information and STA information are backed up

Answer: B