Your company has three offices. An Active Directory site named Site1， Site2， and Site3 exists for each office. You have an Exchange Server 2003 organization. You deploy Exchange Server 2010 servers in Site1. You plan to deploy Exchange Server 2010 servers in Site2 and Site3. You need to recommend a solution that allows the Exchange Server 2010 servers to coexist with the Exchange Server 2003 servers. Your solution must meet the following requirements： .All e-mail messages that are sent to mailboxes on Exchange Server 2003 servers from mailboxes on Exchange Server 2010 servers must be delivered directly from a server in Site2 .All e-mail messages that are sent to mailboxes on Exchange Server 2010 servers from mailboxes on Exchange Server 2003 servers must be delivered directly to a server in Site1 What should you recommend？（）

A. Create two SMTP connectors and one Active Directory SMTP site link.
B. Create a new routing group connector and modify the default routing group connector.
Create an X400 connector to Site1 and modify the cost value for the default routing group connector.
D. Move all Exchange Server 2003 servers and Exchange Server 2010 servers to a single routing group.