Your company has an Exchange 2010 organization that contains multiple Hub Transport servers. You have a line-of-business application that relays e-mail messages by using a Hub Transport servernamed Hub1.  The application only supports sending e-mail to a single SMTP server.  You need to ensure that the application can relay e-mail messages if Hub1 fails.  What should you do？（）

• A、Implement log truncation
• B、Install and configure failover clustering on the Hub Transport servers.
• C、Implement Windows network load balancing on the Hub Transport servers.
• D、Create multiple MX records for the Hub Transport servers in the internal DNS zone.