网络中某些节点的功率是由两侧向其流动，这种节点称为(  )。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69510' and id < 4503178 and id<>'4503178' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69510' and id > 4503178 and id<>'4503178' order by id asc limit 5