[单选题]地面上用微波接力通信系统进行的通信，因系视距传播，平均每（ ）km假设参考电路要经过每跨距约为46km的54次接力转接。

正确答案 ：B

2500

[单选题]A Next Generation Network(NGN) is a () network ,which is able to provide Telecomunication Services ti users and to make use of multiple broadband, QoS-enable transport technologies and in which service-related functions are (下题选择) of the underlying transport-related technologies.

正确答案 ：D

packet-based

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