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The booking notes of the play “The Age of Innocence”:Price:$10BOOKINGThere are four easy ways to book seats for performance:--in personThe Box Office is open from Monday to Saturday, 10 a.m.—8 p.m.--by telephoneRing 01324976 to reserve your tickets or to pay by credit card(Visa, MasterCard and Amex accepted)--by postSimply complete the booking form and return it to Global Theatre Box Office.--on lineComplete the on-line booking form at www.Satan-fiedtheatre.comDISCOUNTS:Saver: $ 2 off any seat booked any time in advance for performances from Monday to Thursday.Savers are available for ch某科技小组的同学们设计了一个自动冲刷装置，该装置能把进水管供给的较小流量的水储存到一定量后，自动开启放水阀门进行冲刷。图是该装置主要部件的截面示意图，AB是一个可以绕O点转动的轻质杠杆，OB=2OA；C是厚度为d、底面积为S的放水阀门（阀门C刚好堵住排水管管口）。将一根细绳一端系在阀门C中央，另一端系在杠杆的A点。浮筒D是一个底面积为4S的空心圆柱体，将细绳一端系在浮筒D下端中央并通过定滑轮使绳的另一端与杠杆的B点相连。当水箱中的水深为2.5h时，系在浮筒D下端的细绳刚好被拉直；当水箱中的水深为3h时，阀门C刚好被打开。在阀门C被打开前，杠杆AB始终保持水平，若细绳所受的重力以及装置的机械阻力均忽略不计，水的密度为ρ水，则放水阀C的质量是多少？