题目

如图所示，三根长度均为L的轻绳分别连接于C、D两点，A、B两端被悬挂在水平天花板上，相距2L，现在C点上悬挂一个质量为M的重物，为使CD绳保持水平，在D点上可施加力的最小值为（          ）                                                                                                              　   A．mg      B．          C．          D．                                                                                                                                     答案：C

查看本题答案和解析