The students should _________ when the teachers give the lessons.

530-321=____

如图所示，“马踏飞燕”是汉代艺术家高度智慧、丰富想象、浪漫主义精神和高超艺术的结晶。飞奔的骏马之所以能用一只蹄稳稳地踏在飞燕上，是因为马的重心位置的竖直线能通过飞燕。有一“马踏飞燕”工艺品采用密度为 8×10³kg/m³的合金材料制造，总体积为1dm³，飞燕与水平桌面的接触面积为20cm²，则该工艺品的质量为____kg，对水平桌面的压强为____Pa。

    Two men walked through the countryside toward another village. As they come to the edge of a river, they saw an old woman sitting there upset because the bridge was____by the storm, and she was too weak to walk across the stream. The first man said____, “We are tall enough, and we can carry you across” The second man thought it troublesome, but he agreed reluctantly（不情愿地）. So the two men ____ the bridge, lifted her between them and carried her across the river. When they got to the other side, they set her down and she went on her way gratefully. After they had walked another mile or so, the second man began to complain “My back began to hurt for lifting her.” The first man ____ smiled and nodded without a word.