Your company has a main office and 20 branch offices.Each office contains an Exchange Server 2010 Mailbox server and an Exchange Server 2010 Hub Transport server. Each office is configured as a separate Active Directory site.Each branch office site has one IP site link that connects to the main office site.You need to ensure that e-mail sent between offices is routed through the Hub Transport servers in the main office. What should you do？（）
- AFrom the Exchange Management Shell， modify the Exchange-specific site link costs.
- BFrom the Exchange Management Shell， configure the main office site as a hub site.
- CFrom Active Directory Sites and Services， modify the site link costs.
- DFrom Active Directory Sites and Services， remove all IP site links and then create new SMTP site links.