Unit4课时跟踪练一

第 1 页共 6 页课时跟踪练(一) Warming Up & Reading — Pre-readingⅠ.阅读理解AEdmund Halley was an English scientist who lived over 200 years ago. He studied theobservations of comets (彗星) which other scientists had made. The orbitof one particular comet was a very difficult mathematical (数学) problem.He could not figure it out. Neither could other scientists who dealt withsuch problems.However, Halley had a friend named Newton, who was a brilliant mathematician. Newtonthough he had already worked out that problem, but he could not find the papers on which he haddone it. He told Halley that the orbit of a comet had the shape of an ellipse (椭圆)．Now Halley set to work. He figured out (解决；计算出) the orbits of some of the comets thathad been observed by scientists. He made a surprising discovery. The comets that had appeared inthe years 1531, 1607, and 1682 all had the same orbit. Yet their appearances had been 75 to 76years apart.This seemed very strange to Halley. The different comets followed the same orbit. The morehalley thought about it, the more he thought that there had not been three different comets, aspeople thought. He decided that they had simply seen the same comet three times. The comet hadgone away and had come back again.It was an astonishing idea! Halley felt certain enough to make a prediction (预言) of whatcomet would happen in the future. He decided that this comet would appear in the year 1758.There were 53 years to go before Halley's prediction could be tested. In 1758 the comet appearedin the sky. Halley did not see it, for he has died some years before. Ever since then that comet hasbeen called Halley's comet, in his honor.语篇解读：本文主要介绍了 200 多年前...