You have a main office and five branch offices. The offices connect to each other by using a WAN link. An Active Directory site exists for each office. Each site has a separate IP site link to all other sites. The main office site is configured as a hub site. You have an Exchange Server 2010 organization. You discover that messages sent between offices are not routed through the Hub Transport servers in themain office. You need to ensure that all messages sent between offices are routed through the Hub Transport serversn the main office. What should you do？（）

A. Change all IP site links to SMTP site links.
B. Modify the Exchange-specific cost for each site link.
C. From the Hub Transport servers in each site，create a journal rule.
D. From the Hub Transport servers in each site，create a transport rule.