astute service providers realize that the continued support of legacy X.25 and asynchronous network element using separate operations network is cost (141) . 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 (142) . Hence, additional maintenance procedures must be maintained and administrative records are (143) . The duplication of transport facilities to carry (144) network traffic is an inefficient use of resources. And not surprisingly, more technologies installed in a central office means the necessity for more physical space and an increase in power connections and power consumption, migration of these (145) network elements to IP-based DCns is alogical strategy.

（144）是（）

A.overlook

B.overlie

C.overlay

D.overleap