全新版大学英语快速阅读第一册Unit8(素文整理).docVIP

Unit 8 I. Directions: Read the following passages, and then select the best choice for each of the questions or incomplete statements. Passage 1 快速阅读自查表 阅读和练习应完成的时间：5分22秒 实际完成时间： 做对的练习题数记录： One of the greatest mysteries in biology-how the monarch butterfly (帝王蝶) travels thousands of kilometers on its yearly migration (迁移)-has just been solved. Monarch butterflies use the sun to set their body clocks and make their journeys, according to US scientists. No other butterfly in the world migrates like the orange and black monarchs of North America. They cannot live for long periods in cold weather. Each autumn, thousands travel up to 3,000 km to spend the winter in the mountains of Mexico. There are so many, they almost block out the sky, and you can hear their wings beating. It usually takes the butterflies two months to reach Mexico. After staying five months, they head back up north in the spring. But not one butterfly finishes the whole round-trip. They lay eggs along the way and die. Three generations of butterflies will live and die during the spring journey alone. The fourth and final generation of the year is born in early autumn and will reach the north. But it hardly gets to rest before starting the long journey south to Mexico. The most amazing thing about these butterflies is that they return to the very same tree in Mexico that their great-great-grandparents used the winter before. Past studies have shown that the insects use the sun as a compass (指南针) to show them the way. But experts are unsure how the butterflies change their direction as the sun moves in the sky. This new study now shows that the insects use a “circadian (生理节奏的)” clock in their bodies as part of their sun compass. In laboratory tests, monarch butterflies were found to fly in the right direction under normal daylight hours. But those flying in 24-hour light headed straight towards the sun. That is, they no longer had any sense of time. Scientist Steven Reppert, wh