Your Exchange Server 2010 organization contains the servers shown in the following table. Server1 and Server2 are members of a database availability group （DAG）.You shut down  Server1.Some users report that they cannot access their mailboxes.You need to ensure that all users can connect to their mailboxes if a single Mailbox server becomes unavailable.What should you do？（）

• A、Create a Client Access server array.
• B、Configure the shadow redundancy settings.
• C、Remove the Hub Transport server role from Server1.
• D、Add mailbox database copies to Server1 and Server2.