核酸的基本组成单位是（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='30913' and id < 2487669 and id<>'2487669' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='30913' and id > 2487669 and id<>'2487669' order by id asc limit 5