题目

图中弹簧秤、绳和滑轮的重量均不计，绳与滑轮间的摩擦力不计，物体的重力都是G，在图甲、乙、丙三种情况下，弹簧秤的读数分别是F1、F2、F3，则（                                                        ）                                                        　   A． F3＞F1=F2           B．F3=F1＞F2    C． F1=F2=F3       D． F1＞F2=F3                                                                                                                                   答案：B

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