How should you configure HaContoso?

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 Secondary only.
• 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 Secondary only.
• 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:
http://msdn.microsoft.com/en-us/library/ff877884.aspx