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.