如图是某实际电压源的外特性曲线，则该电源的等效内阻等于（）。 

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SQL Error: select id,body,options from ***_enewstiku where sourceid='32670' and id < 2598688 and id<>'2598688' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='32670' and id > 2598688 and id<>'2598688' order by id asc limit 5