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【单选题】
如图所示,在两块相同的竖直木块之间,有质量均为 m 的 4 块相同的砖,用两个大小均为 F 的水平力压木板,使砖静止不动,则第 2 块砖对第 3 块砖的摩擦力大小为 ( )A.
0
B.
mg
C.
mg/2
D.
mg/4
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