Which server should you add to the HOSTS file on Server5?

Your network has a Lyric Server 2010 infrastructure that contains five servers.
The servers are configured as shown in the following table.

On Server5, you plan to use a custom HOSTS file for name resolution.
You need to ensure that Server5 can be used as a reverse proxy for the Lync Server infrastructure.
Which server should you add to the HOSTS file on Server5?

A.
Server1

B.
Server2

C.
Server3

D.
Server4

Explanation:
http://www.agileit.com/Blog/Lists/Posts/Post.aspx?ID=792

http://technet.microsoft.com/en-us/library/gg429719.aspx