Your network contains an internal network and a perimeter network. The internal network contains a single Active Directory site. 
The perimeter network contains two Exchange Server 2010 Edge Transport servers. You plan to deploy an Exchange Server 2010 organization on the internal network. 
You need to plan the deployment of Hub Transport server roles to meet the following requirements：.If a single Hub Transport server fails， e-mail messages from the Internet must be delivered to the Mailboxservers.
.If a single Hub Transport server fails， users must be able to send e-mail messages to other users thathave mailboxes on the same Mailbox server. 
What should you include in the plan？（）

You have a Microsoft Internet Security and Accelerator （ISA） 2006 server that provides all Internet accessfor your company. 
You have two Mailbox servers configured in a database availability group （DAG）， two Client Accessservers， and two Hub Transport servers. 
You need to recommend changes to the environment to ensure that users can access Outlook Web App（OWA） from the Internet if any single server fails. 
What should you recommend？（）