题目

在同一地理位置上，甲、乙两个单摆的摆动图象如图所示，则下列论断正确的是（ ） ①两摆球在最低点的速度大小相等②两摆球在最低点对悬线拉力大小相同③两摆球在最低点加速度大小相等④两摆球在最低点动能相等． A . ①②③④ B . ①②③ C . ①③ D . ①④ 答案：CThe terrible earthquake ______ when I _______some cleaning.A.starts, was doingB.started, was doingC.was starting, was doingD.starts, were doing