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．X.21

B．X.25

C．X.28

D．X.29

投资者通过上海证券交易所交易系统投票时，股东大会有多个待表决的议案的，可以按照任意次序对各议案进行表决申报。对同一议案不能多次进行表决申报，多次申报的，以第一次申报为准。( )