下列氨基酸中哪一种提供一碳单位（    ）

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SQL Error: select id,body,options from ***_enewstiku where sourceid='27519' and id < 2271253 and id<>'2271253' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='27519' and id > 2271253 and id<>'2271253' order by id asc limit 5