题目

Children under sixteen are forbidden to see such films _____ bad for their mental development.   A. that is   B. that are  C. as is      D. as are 答案：D 如图所示，质量为m的小球固定在长为l的细杆一端，绕细杆的另一端O在竖直面内做圆周运动，球转到最高点A时，线速度大小为，则 A．杆受到mg/2的拉力 B．杆受到mg/2的压力 C．杆受到3 mg/2的拉力 D．杆受到3 mg/2的压力