● astute service providers realize that the continued support of legacy X.25 and asynchronous network elements using separate operations network is cost ___(71)___.for example, the maintenance of multiple networks can require additional staff. often, this staff must be trained on multiple vendor technologies, sometimes requiring parallel groups specializing in each ___(72)___ hence, additional maintenance procedures must be maintained and administrative records are ___(73)___ the duplication of trasport facilities to carry ___(74)___ network traffic is an inefficient use of resources and, not surprisingly, more technologies installed in a central office mean the necessity for more physical space, and an increase in power connections and power consumption. migration of these ___(75)___ network elements to IP-based DCns is alogical strategy . 
　　(71) A．prohibitive        B．feasible                   C．connective                     D．special 
　　(72) A．line                         B．platform                  C．sever                      D．switch 
　　(73) A．declined                  B．proliferated              C．destroyed                D．produced
　　(74) A．overlook                 B．overlie　　　　      C．overlay                   D．overleap 
　　(75) A．traditional                B．dominancy              C．redundancy             D．legacy