You create an availability group named HaContoso that has replicas named Server01/HA, Server02/HA, and
Server03/HA.
Currently, Server01l/HA is the primary replica.
You need to ensure that the following requirements are met:
Backup operations occur on Server02/HA.
If Server02/HA is unavailable, backup operations occur on Server03/HA.
Backup operations do not occur on Server01/HA.
How should you configure HaContoso?

A.
Set the backup preference of HaContoso to Prefer Secondary.
Set the backup priority of Server02/HA to 20.
Set the backup priority of Server03/HA to 10.

B.
Set the backup preference of HaContoso to Secondaryonly.
Set the backup priority of Server02/HA to 20.
Set the backup priority of Server03/HA to 10.

C.
Set the backup preference of HaContoso to Secondaryonly.
Set the backup priority of Server02/HA to 10.
Set the backup priority of Server03/HA to 20.

D.
Set the exclude replica of Server01/HA to true.
Set the backup priority of Server02/HA to 10.
Set the backup priority of Server03/HA to 20.

Explanation:
Reference: http://msdn.microsoft.com/en-us/library/ff877884.aspx