图9所示电路，开关合上，电路中的时间常数（     ）。 

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='68473' and id < 4421001 and id<>'4421001' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='68473' and id > 4421001 and id<>'4421001' order by id asc limit 5