现代社会中，( )早已成为推动整个经济社会发展的最重要动力。

A．资源

B．劳动力

C．技术

D．城市

Frame Relay is simplified form of (71) ,similar in principle to (72) , in which synchronous, frames of data are routed to different destinations depending on header information. Packets are routed throught one or more Virtual Circuits known as (73) . Most Virtual Circuits are (74) ,which means that the network provider sets up all DLCI connections at subscription time. (75) are also part of the Frame Relay specification. They privide a link that only lasts only as long as the session.

A．DLCIs

B．HDLCs

C．SDECs

D．DLs