直流电动机按励磁方式分为（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='30222' and id < 2444798 and id<>'2444798' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='30222' and id > 2444798 and id<>'2444798' order by id asc limit 5