Astute service providers realize that the continued support of legacy X.25 and asynchronous network element using separate operations network is cost（1）. 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（2）hence,additional maintenance procedures must be maintained and administrative records are（3）the duplication of trasport facilities to carry（4）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（5）network elements to IP-based DCns is alogical strategy

4（）

A.overlook 

B.overlie 

C.overlay 

D.overleap

用于抢救高血压危象及难治性心力衰竭的是（）。

A.美托洛尔

B.氯沙坦

C.卡托普利

D.硝普钠

E.氨氯地平