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.