材料一：1851年5月1日，世界上第一次博览会在英国召开。完成了工业革命的英国已经是世界上一流的强国，没有人怀疑英国的强大，因而强大而带来的巨大召唤力使英国举办了世界上第一届世界博览会。……许多参观者在这里看到了他们平时绝无可能看到的商品，看到了这些神奇的机器承担以往只能靠人工而无法借助机械的帮助来完成的工作……这次世界博览会不仅是一次“眼花缭乱，丰富多彩”的陈列，而且开创了今后数十年自由贸易的先驱，向人类预示了工业化生产时代的到来。

材料二：1992年意大利热那亚世博会的主题是：船舶与海洋，右图是其吉祥物及标志，其标志上有“Colombo^，92”、“500”字样。

材料三：见下图

要测量小明通过楼梯上楼时的功率，不需要测量的是（   ）               

—What are you ___________?

—My keys. I can't find them.

    Most American families like to have a vacation in summer. Summer is a good season for vacation. It is often hot in July and August.

    Children do not go to school in those two months. Some people like to stay at home, read books, or watch TV. Many families take their lunch to eat at a place with many trees or a nice lake. Some people have enough time and money to travel to other countries like France, Japan and Australia. They usually fly to these countries. Many families travel by car or train to see interesting places in their own countries. Their favorite city is New York.

    Not everyone likes to go to busy cities. Some families travel to mountains or beautiful valleys（山谷）.