理想电压源的源电压为U,则其内阻为（）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='32670' and id < 2598662 and id<>'2598662' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='32670' and id > 2598662 and id<>'2598662' order by id asc limit 5