D is corrent. A wide area network (WAN) is the best kind of network because it can connect many sites located across a broad geographical distance.
A is incorrect. A value-added network (VAN) is, in general, more expensive than a private network such as WAN for high-volume communications.
B is incorrect. A local area network (LAN) is generally limited to short distances (e.g., 2,000 feet radius of the servers).
C is incorrect. A private branch exchange (PBX) is an electronic switch that transfers telephone calls, which does not have the network capabilities needed by the company.
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