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. A.ISDN B.ATM C.circuit-based D.packet-based 请帮忙给出正确答案和分析，谢谢！
