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  3. There have been several claims to have cloned humans over the past few years. Most have been bogus. But the announcement made th

There have been several claims to have cloned humans over the past few years. Most have been bogus. But the announcement made th

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问题     There have been several claims to have cloned humans over the past few years. Most have been bogus. But the announcement made this week by Woo Sur Hwang, of Seoul National University in South Korea, and his colleagues, is serious. It is the first to achieve the accolade of publication in a peer-reviewed scientific journal. Dr. Hwang’s work appears in Science.
    The terminology of human development has become slippery over the past few years, in the hands of both "life-begins-at-conception" propagandists who want to stop this sort of research, and publicity-seeking scientists who have claimed more than they have really achieved. What Dr. Hwang and his team have created is not what developmental biologists would normally refer to as an embryo. But it is a genuine scientific advance. South Korea’s researchers have taken egg cells from volunteer women, removed the nuclei from those cells (which contain only half of the genetic complement required to make a human being, since the other half is provided by the sperm), and replaced each nucleus with one taken from one of the volunteer’s body cells (which contains a full genetic complement). Given a suitable chemical kick-start, such re-nucleated cells will begin dividing as though they were eggs that had been fertilised in the more traditional manner. Since they have all of the mother’s genes, they count as clones.
    Then the team cultured the dividing eggs until they had formed structures called blastocysts, with a few dozen cells each. This is the significant advance. At this stage the structure, though still just a featureless ball of cells, has started to differentiate into the body’s three basic cell types (known as endoderm, mesoderm and ectoderm). The researchers were able to extract cells from some of their blastocysts, and grow tissues containing all three cell types.
    These are so-called stem cells, which can be directed to form a wide variety of the specialised cells from which organs are built. That, not the creation of new human beings, is the stated reason for this sort of research, since specialised cells made this way might be used to replace the cells lost in diseases such as Parkinson’s and type-I diabetes. This process is known as therapeutic cloning.
    No doubt Dr Hwang’s scientific success will sharpen the debate between those who see therapeutic cloning as a potential force for good, and those who see it as a step on the road to a cloned human being. The former have been queuing up to praise the scientist’s work. It is "a major medical milestone" that could help spur a "revolution", said Robert Lanza, a cloning expert.
    But opponents of therapeutic cloning should not worry too much yet. The road from a blastocyst to a baby is a long and complex one. Nevertheless, the South Korean breakthrough make’s it more urgent than ever that legislation be passed differentiating clearly between therapeutic and reproductive cloning—permitting the former and prohibiting the latter.
The South Korean team’s breakthrough in cloning is that______.
选项 A、they have really created an embryo
B、they have developed women’s body cells into blastocysts
C、they have cultivated blastocysts with fixed features
D、they have been able to grow tissues containing stem cells
答案D
解析 细节题。此题需要认真阅读文章中有关韩国的克隆研究内容部分。从第二段中部开始，我们得知，韩国科学家从志愿的妇女身体上取得卵细胞，去除其中的核子，代之以该志愿者的体细胞中取出的核子。通过化学的方法，被重新置人体细胞核子的卵细胞开始分裂，就好像是以传统的方式“授精”了一样。(由此可知B明显不对。)然后研究小组将分裂的卵细胞进行培养直到它们形成一种叫blastocyst的结构，这种结构此时只是没有任何面貌身体特点的细胞球(C与这点不符合，所以不对)，但开始分化形成身体所需的三种基本细胞。因此研究人员可以从blastocyst结构中提取细胞，培养成含有这三种细胞的组织。这些干细胞可以通过培养形成各种用于构建器官的特殊细胞。通过以上分析可知，D是正确答案。
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