You are the messaging engineer for your company. Your company has a main office and a branch office. The main office has 2,500 users. The branch office has 1,200 users.

The network consists of a single Active Directory domain. The Active Directory domain contains three domain controllers. An Active Directory site exists for each office. The domain controllers and their relevant configurations are shown in the following table:

You plan to deploy Exchange Server 2007 Mailbox servers in each site.

You need to recommend changes to the Active Directory infrastructure to support Exchange Server 2007. Your recommendation should meet the following requirements:

Host name resolution should be redundant.

If a single global catalog server fails, the Exchange Server 2007 servers should be unaffected.

If a single domain controller fails, the Exchange Server 2007 servers should be unaffected.

If a WAN link fails, users must be able to access their local Mailbox server.

Which three changes should you recommend? (Each correct answer presents part of the solution. Choose three.)

A.
Configure all domain controllers to be DNS Servers.

B.
Configure DC01 and DC03 to be WINS servers.

C.
Configure DC02 and DC03 to be global catalog servers.

D.
Move the PDC emulator operations master role to DC03.

E.
Install an additional domain controller in the branch office and configure it to be a global catalog server.

Explanation:
1. Redundant host name resolution. Requires A.

2. If single GC fails, Exchange should be unaffected. Requires C.

3. If single DC fails, Exchange should be unaffected. Requires E.

4. If WAN link fails, users can access their local Mailbox server. Requires E.

http://www.msexchange.org/articles-tutorials/exchange-server-2007/planning-architecture/how-exchange-server-2007-core-services-work-together.html