710分大学英语同步水平练与考

章节摘录

　　In a separate development, all international team of scientists, headed by Gerta Keller of Princeton Univ. in New Jersey, called into question the notion that a massive asteroid strike off the Yucatan peninsula （ in Mexico） was solely responsible for the extinction of the dinosaurs 65million years ago. The researchers, who published their observations in the Proceedings of the National Academy of Sciences, said that new measurements indicate the Chicxulub crater off Mexico was actually created some 300,000 years before the dinosaurs became extinct. The teamargued that the Chicxulub impact event contributed to the extinction, but that a second, as yetun found, impact actually finished off the dinosaurs. Many scientists, however, continue to believe that the Yucatan impact was responsible for the extinction of the dinosaurs on its own.　　Biologists in Japan, led by Tomohiro Ko no of Tokyo Univ. of Agriculture, produced a healthy mouse from two eggs, neither fertilized by a sperm cell, according to their report in Nature April 22. In some species, unfertilized eggs can grow into full animals, a phenomenon called parthenogenesis. This occurs among some insects, fish, birds, and other animals, but never until the work of the Japanese team among mammals. （Unlike in nature aloccurrences of parthenogenesis, the mouse received chromosomes from eggs from two different females. ） Kono and his colleagues inactivated a gene in one of the eggs that contributed to the makeup of the mouse and in doing so, caused the egg to behave more like a sperm cell. The"mouse with two moms" was called Ka guya, after a princess in a Japanese fairy tale. The teamcreated only two healthy mice out of nearly 600 attempts.

书籍目录

College English Test 1College English Test 2College English Test 3College English Test 4College English Test 5College English Test 6College English Test 7College English Test 8College English Test 9College English Test 10参考答案和高分范文

作者简介

《710分大学英语同步水平练与考(第2版)(4级)》根据国家教育部高教司主持和领导下的大学英语四、六级考试改革项目组和考试委员会制定的《全国大学英语四、六级考试改革方案（试行）》和《大学英语课程教学要求（试行）》，依据全国大学英语四、六级2005年6月考试所采用的710分计分体制来编写的。该系列与大学英语教学课程和教学要求同步，由浅入深、循序渐进，一学期一册，共分四级。《710分大学英语同步水平练与考(第2版)(4级)》的难易程度与《全新版大学英语》、《新视野大学英语》、《大学英语》、《新编大学英语》、《21世纪大学英语》、《当代大学英语》和《大学核心英语》等同级教材一致，可作上述教材的同步辅导材料。

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