You have an Exchange organization.All servers in the organization have Exchange Server 2010 Service Pack 1 （SP1） installed. The organization contains a database availability group （DAG） named DAG1.DAG1 contains two Mailbox servers named Server1 and Server2.Five mailbox databases are replicated in DAG1.You need to install Exchange rollup updates on Server1.The solution must not prevent users from accessing their mailboxes. What should you do first？（）
- ARun the Set-DatabaseAvailabilityGroup cmdlet， and then enable Datacenter Activation Coordination for DAG1.
- BRun the Set-MailboxDatabase cmdlet， and then configure all mailbox database copies as lagged copies.
- CRun the Suspend-MailboxDatabaseCopy cmdlet， and then switch over all mailbox databases to Server2.
- DRun the Update-MailboxDatabaseCopy cmdlet， and then modify the mailbox database Activation preference.