You have an Exchange Server 2010 organization. The network contains an Exchange Server 2010 Mailbox server named Server1. All mailboxes are stored on Server1. You perform a Typical installation of Exchange Server 2010 on a new server named Server2. You plan to implement redundancy for mailbox access. You need to recommend a solution that ensures that client computers can reconnect to their mailboxwithin five minutes if Server1 fails. What should you recommend？（）
- AConfigure cluster continuous replication （CCR）. Implement a file share witness.
- BConfigure a Network Load Balancing cluster that includes Server1 and Server2. Implement Active Directory-integrated DNS zones.
- CConfigure a database availability group （DAG） that includes Server1 and Server2. Set the time to live （TTL） for the DNS record.
- DConfigure a database availability group （DAG） that includes Server1 and Server2. Use the same certificate for both servers.