巨幼红细胞性贫血是由于缺少（ ）。

试卷相关题目

SQL Error: select id,body,options from ***_enewstiku where sourceid='31124' and id < 2501315 and id<>'2501315' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='31124' and id > 2501315 and id<>'2501315' order by id asc limit 5