What would happen to an RDS (Relational Database Service) multi-Availability Zone deployment of the primary OB instance fails?

What would happen to an RDS (Relational Database Service) multi-Availability Zone deployment of the primary
OB instance fails?

A.
The IP of the primary DB instance is switched to the standby OB instance

B.
The RDS (Relational Database Service) DB instance reboots

C.
A new DB instance is created in the standby availability zone

D.
The canonical name record (CNAME) is changed from primary to standby