[本科]载波通道传输通信速率低，一般用来传送状态（逻辑）信号，用于构成（    ）。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69487' and id < 4500917 and id<>'4500917' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69487' and id > 4500917 and id<>'4500917' order by id asc limit 5