题目

如图所示，粗糙水平桌面上有一质量为m的铜质矩形线圈.当一竖直放置的条形磁铁从线圈中线AB正上方等高快速经过时，若线圈始终不动，则关于线圈受到的支持力FN及在水平方向运动趋势的正确判断是 A．FN先小于mg后大于mg,运动趋势向左 B．FN先大于mg后小于mg,运动趋势向左 C．FN先大于mg后小于mg,运动趋势向右 D．FN先大于mg后大于mg,运动趋势向右 To us it seems so natural to put up an umbrella to keep the water off when it rains. But actually the umbrella was not invented as protection against the rain. Its first use was as a shade against the sun! Nobody knows who first invented it, but the umbrella was used in very ancient times. Probably the first to use it were the Chinese, back in the eleventh century B.C. We know that the umbrella was used in ancient Egypt and Babylon as a sunshade. And there was a strange thing connected with its use: it became a symbol of honor. In the Far East in ancient times, the umbrella was allowed to be used only by those in high office. In Europe, the Greeks were the first to use the umbrella as a sunshade. And the umbrella was in common used in ancient Greece. But it is believed that the first persons in Europe to use the umbrella as protection against the rain were the ancient Romans. During the Middle Ages, the use of the umbrella practically disappeared. Then it appeared again in Italy in the late sixteenth century. And again it was considered as a symbol of power. By 1680, the umbrella appeared in France, and later on in England. By the eighteenth century, the umbrella was used against rain throughout most of Europe. Umbrellas have not changed much in style during all this time, though they have become much lighter in weight. It wasn’t until the twentieth century that women’s umbrellas began to be made, in a whole variety of colours. 1.According to this passage, the umbrella was probably first invented in ancient _______. A. China         B. Egypt       C. Greece         D. Rome 2.Which of the following statements is not true about the umbrella? A. No one exactly knows who was the inventor of the umbrella. B. The umbrella was first invented to be used as protection against the sun. C. The umbrella changed much in style in the eighteenth century. D. In Europe, the Greeks were the first to use the umbrella as a sunshade. 3.A strange feature(特征) of the umbrella’s use is that it was used as _______. A. protection against rain                    B. a shade against the sun C. a symbol of honour and power              D. women’s decoration 4.In Europe, the umbrella was first used against the rain ___________. A. during the Middle Ages   B. by the eighteenth century   C. in Rome   D. in Greece