公共英语PETS二级阅读复习(33) The first cloning experiments in the 1950s involved frogs and toads. It was not until 1997 that scientists successfully cloned the first mammal, the now world-famous sheep known as Dolly. Cloning techniques have continued to improve since then, and today there are cloned mice, salmon, and cattle. 克隆实验开始于20世纪50年代，对象为青蛙和蟾蜍。直到1997年，科学家才成功地克隆了哺乳类动物，即世界闻名的“多莉羊”。克隆技术从那时起得到了持续的进展，今天已有了克隆老鼠、克隆鲑鱼和克隆牛。www.Ｅxamda.CoM考试就到百考试题 公共英语PETS二级阅读复习(34) Saving lives has always been an important mission of science. Now science, and indeed all society, is facing a new dilemma: whether or not to try and save more lives through human cloning. 挽救生命一直是科学研究的一项重要使命。如今，科学研究，其实是整个社会，正面临着一个新的困境：是否要设法通过克隆人类来挽救更多的生命。 更多信息：09年公共英语四级听力应试指导及应试技巧 全国公共英语四级考试笔试试卷内容与结构