Which components should you recommend adding to the network?

Your network has a Lync Server 2010 infrastructure that contains the following servers:
* Two Edge Servers
* One Mediation Server
* One reverse proxy server
* Three Enterprise Edition servers in a Front End pool
You need to recommend changes to ensure that the Address Book service for remote users is available if a single server fails. The solution must minimize costs. Which components should you recommend adding to the network?

A.
one Mediation Server and one hardware load balancer

B.
one Mediation Server and DNS load balancing

C.
one reverse proxy server and one hardware load balancer

D.
one reverse proxy server and DNS load balancing

Explanation:
The reverse proxy is required for the following:
* To allow users to connect to meetings or dial-in conferences using simple URLs
* To enable external users to download meeting content
* To enable external users to expand distribution groups
* To allow the user to obtain a user-based certificate for client certificate based authentication
* To enable remote users to download files from the Address Book Server or to submit queries to the Address Book Web Query service
* To enable remote users to obtain updates to client and device software
Regardless of whether you use hardware load balancing for your Edge Server pool, you will need a hardware load balancer if there are two or more reverse proxy servers deployed.
(http://technet.microsoft.com/en-us/library/gg425779.aspx)