电路如图3所示，电路中电压 U 等于（      ）。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='68474' and id < 4421084 and id<>'4421084' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='68474' and id > 4421084 and id<>'4421084' order by id asc limit 5