一个步行周期是指（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='25667' and id < 2157181 and id<>'2157181' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='25667' and id > 2157181 and id<>'2157181' order by id asc limit 5