The multinational corporation Certkiller has large campuses in the US, Guatemala, and Singapore. There are about 15,000 phones at each location. A call pattern survey discovers that almost all calls are intra-site. Which is the most appropriate deployment option for Certkiller ?

A.
Single site deployment with connections to the PSTN.

B.
Distributed call processing with an improved WAN infrastructure.

C.
Single site deployment with clusters connected via infrastructure trunks.

D.
Centralized call processing with one location chosen as the call processing center.