求下图(a) 图，开关S 断开和闭合时A 点电位U 为 (     )。 (a) (a)

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69437' and id < 4496795 and id<>'4496795' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69437' and id > 4496795 and id<>'4496795' order by id asc limit 5