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一、选择题 1.地面上的物体受到的重力 A.其作用点一定在物体上 B.其方向垂直于接触面地面的压力 ( )C.是由地球的吸引力产生的 D.就是物体对
First, the multiple-choice questions 1. The ground on the subject of gravity A. The role of the point must be on the object B. Its direction perpendicular to the contact surface of the ground pressure () C. Is generated by the Earth’s attraction D. Is the object pair