求一端口的等效电阻时，用外施电压法的电路为（   ）。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69473' and id < 4501195 and id<>'4501195' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69473' and id > 4501195 and id<>'4501195' order by id asc limit 5