根据皮亚杰的认知发展阶段理论，个体在（ ）思维开始具有可逆性。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='32260' and id < 2568599 and id<>'2568599' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='32260' and id > 2568599 and id<>'2568599' order by id asc limit 5