经济周期的实质是（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='31437' and id < 2520216 and id<>'2520216' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='31437' and id > 2520216 and id<>'2520216' order by id asc limit 5