OSI参考模型中完成路由选择功能的层次是（）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='30263' and id < 2448173 and id<>'2448173' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='30263' and id > 2448173 and id<>'2448173' order by id asc limit 5