下图所示电路，其戴维南等效内阻及为（）。 

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SQL Error: select id,body,options from ***_enewstiku where sourceid='32630' and id < 2594674 and id<>'2594674' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='32630' and id > 2594674 and id<>'2594674' order by id asc limit 5