Select the correct statement(s) regarding CENTREX. a. CENTREX systems reside at the service providers central office, however, the operations and maintenance are still the responsibility of the user organization b. CENTREX systems reside at the service providers central office, and the operations and maintenance responsibilities belong to the service provider c. CENTREX systems offer greater choice to users because the service provider has better and more sophisticated equipment than single organizations have d. All are correct

CENTREX systems reside at the service providers central office, and the operations and maintenance responsibilities belong to the service provider

Explanation:

CENTRal EXchange. Telephone company service that obviates the need of buying, maintaining, and upgrading a private branch exchange (PBX). Basically, Centrex service consists of ordinary trunk-lines to which several features are added by the phone company. While it is  more economical than a PBX system, it often requires special telephone equipment for exploiting its features.

Based on the above definition, we can infer that CENTREX systems reside at the service providers central office, and the operations and maintenance responsibilities belong to the service provider is the correct option since features are usually added by the company.

i believe the two important functions that skype uses are nat traversal and user location.good luck        

explanation: