You have an Exchange Server 2010 organization that contains a database availability group （DAG） named DAG1.DAG1 contains five Mailbox servers including a server named MBX1.MBX1 fails.You plan to perform a recovery installation of MBX1.You need to ensure that the restored server can become a member of DAG1.The solution must ensure that mailbox databases are available if a single server fails.What should you do？（）
- ARemove MBX1 from DAG1.
- BRemove all mailbox database copies from DAG1.
- CRemove the computer account for MBX1 from Active Directory.
- DRun the Clean-MailboxDatabase cmdlet on all other members of DAG1 except MBX1.