You plan to deploy an Exchange Server 2010 Client Access server on a new server. The server will be a member of a database availability group (DAG).

You need to identify the operating system required for the planned deployment. The solution must minimize software costs.

Which operating system should you identify?

A.
Windows Server 2008 R2 Foundation.

B.
Windows Server 2008 R2 Standard.

C.
Windows Server 2008 Service Pack 2 (SP2) Enterprise.

D.
Windows Server 2008 Service Pack 2 (SP2) Web.

Explanation:
DAGs use Windows Failover Clustering technology, and as a result, they require the Enterprise version of Windows.

Reference:

http://technet.microsoft.com/en-us/library/dd638104.aspx#SoftReq