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.
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.