电路如图所示，求电路的时间常数τ为（）。 

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SQL Error: select id,body,options from ***_enewstiku where sourceid='32672' and id < 2598922 and id<>'2598922' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='32672' and id > 2598922 and id<>'2598922' order by id asc limit 5