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．Permanent Circuits

B．Permanent Virtual Circuits

C．Switched Virtual Circuits

D．Switched Circuits

一名队员可以佩戴饰物进行比赛吗？（）

A.可以

B.不可以

C.由竞赛规程决定

D.由裁判员决定