You deploy an Exchange organization.All servers in the organization have Exchange Server 2010 Service Pack 1 （SP1） installed.The organization contains two Hub Transport servers.The network contains two Active Directory sites named Site1 and Site2.Each site contains one Hub Transport server.Each site has a direct connection to the Internet.You need to configure message routing for the organization to meet the following requirements：   （1）E-mail messages sent to a SMTP domain named nwtraders.com must be delivered from Site2.   （2）If Site2 is unavailable， e-mail messages sent to nwtraders.com must be delivered from Sitel.  （3）E-mail messages sent to all other SMTP domains must be delivered from Sitel only.  What should you do？（）

• A、Create two Send connectors.Assign one Hub Transport server as a source server to each Send connector.Configure the connectors as Scoped send connectors.
• B、Create one Send connector.Assign both Hub Transport servers as source servers.Configure the connector as a Scoped send connector.
• C、Create one Send connector.Assign both Hub Transport servers as source servers.Configure the address spaces for the connector， and then configure the costs for the address spaces.
• D、Create two Send connectors. Assign one Hub Transport server as a source server to each Send connector.Configure the address spaces for each connector.