请描述一下这个详细配置，谢谢

guangyishikong

You work as the network Exchange administrator at Certkiller.com. The Certkiller.com network consists of a single Active Directory domain named Certkiller.com. All server on the Certkiller.com network run Windows Server 2003 and all client computers run Windows XP Professional. The Certkiller.com network contains a two-node active/passive cluster.
The Certkiller.com network users complain during the course of the day about performance deteriorating when accessing the server using Outlook Web Access whilst the support group reports uptime is excellent. You obtain two new servers to help this performance deteriorating problem
You are required to choose which configuration will best improve performance for the Certkiller.com network users
What should you do?
A    The two servers must be configured as front-end active/active cluster
B   The two servers must be configured to use Network Load Balancing in the back of a front-      end/back end configuration with the existing cluster as the front-end
C   The two servers must be configured to use Network Load Balancing in the back of a front-end/back end configuration with the existing cluster as the back-end
DThe two servers must be joined to the existing cluster as passive members
答案：C
请描述一下这个详细配置，谢谢 。为什么