DNA的二级空间结构是（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='31090' and id < 2499928 and id<>'2499928' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='31090' and id > 2499928 and id<>'2499928' order by id asc limit 5