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:
According to these references, this answer looks correct.
Reference:
http://msdn.microsoft.com/en-us/library/ff877884.aspx
http://msdn.microsoft.com/en-us/library/hh245119.aspx
http://msdn.microsoft.com/en-us/library/hh710053.aspx