Answer:
CENTREX systems reside at the service providers central office, and the operations and maintenance responsibilities belong to the service provider
Step-by-step 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.