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    A new study says that American children have exciting after-school life. Many junior and senior students have a lot of interesting things to do in their free time. About 57% students have activities every day. 82% students have activities at least four times a week. American students spend their free time doing sports or enjoying arts, music and dancing. They like to have fun outside school because they can make a lot of friends during their activities.

图7 是甲、乙两种物质的质量和体积的关系图像。若用质量相等的甲、乙两种物质分别制成实心正方体A、B，把它们平放在水平地面上，则两正方体A、B对水平地面的压强之比为 (    )