You work as the enterprise exchange administrator at Company.com.The Company.com network consists of a single Active Directory domain named Company.com.Company.com has an Exchange Server 2010 organization.Company.com contains three servers named -sr11， -sr12 and -sr13.these servers are configured as follows：-sr11 has the front-end role installed and is running exchange server 2003 service pack 2.-sr12 has the back-end role installed and is running exchange server 2003 service pack 2.-sr13 has the client access role and the mailbox role installed and is running exchange server 2010.you have received instructions from the cio to move the mailboxes from -sr12 to -sr13.however， you need to make sure thag the users can use the e-mail facilities.What should you do？（）

A. You should consider installing the Exchange Server 2010 Edge Transport server role.
B. You should consider removing the Exchange Server 2003 servers.
C. You should consider installing a new Exchange Server 2010 Client Access server and remove the Exchange Server 2003 front-end server.
D. You should consider installing the Exchange Server 2010 Hub Transport server role.