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  3. [A] The work builds on a study published

[A] The work builds on a study published

tikufree2020-05-20  25
问题 [A] The work builds on a study published last year by Shinya Yamanaka of Kyoto University in Japan, which showed that mouse tail cells could be transformed into ES-like cells by inserting four genes (Science Now, 3 July 2006).Those genes are normally switched off after embryonic cells differentiate into the various cell types. In June this year, Yamanaka and another group reported that the cells were truly pluripotent, meaning that they had the potential to grow into any tissue in the body (Science Now, 6 June).　　[B] In the new work, Yamanaka and his colleagues used a retrovirus to ferry into adult cells the same four genes they had previously used to reprogram mouse cells: OCT3/4, SOX2, KLF4, and c-MYC. They reprogrammed cells taken from the facial skin of a 36-year-old woman and from connective tissue from a 69-year-old man. Roughly one iPS cell line was produced for every 5,000 cells the researchers treated using the technique, an efficiency that enabled them to produce several cell lines from each experiment.　　[C] Now the race to repeat the feat in human cells has ended in a tie: Two groups report today that they have reprogrammed human skin cells into so-called induced pluripotent cells (iPSs). In a paper published online in Cell, Yamanaka and his colleagues show that their mouse technique works with human cells as well. And in a paper published online in Science, James Thomson of the University of Wisconsin, Madison, and his colleagues report success in reprogramming human cells, again by inserting just four genes, two of which are different from those Yamanaka uses.　　[D] Once the kinks are worked out, “the whole field is going to completely change,” says stem cell researcher Jose Cibelli of Michigan State University in East Lansing. “People working on ethics will have to find something new to worry about.”　　[E] Thomson’s team started from scratch, identifying its own list of 14 candidate reprogramming genes. Like Yamanaka’s group, the team used a systematic process of elimination to identify four factors: OCT3 and SOX2, as Yamanaka used, and two different genes, NANOG and LIN28. The group reprogrammed cells from fetal skin and from the foreskin of a newborn boy. The researchers were able to transform about one in 10,000 cells, less than Yamanaka’s technique achieved, Thomson says, but still enough to create several cell lines from a single experiment.　　[F] Scientists have managed to reprogram human skin cells directly into cells that look and act like embryonic stem (ES) cells. The technique makes it possible to generate patient-specific stem cells to study or treat disease without using embryos or oocytes—and therefore could bypass the ethical debates that have plagued the field. “This is like an earthquake for both the science and politics of stem cell research,” says Jesse Reynolds, policy analyst for the Center for Genetics and Society in Oakland, California.　　[G] Although promising, both techniques share a downside. The retroviruses used to insert the genes could cause tumors in tissues grown from the cells. The crucial next step, everyone agrees, is to find a way to reprogram cells by switching on the genes rather than inserting new copies. The field is moving quickly toward that goal, says stem cell researcher Douglas Melton of Harvard University. “It is not hard to imagine a time when you could add small molecules that would tickle the same networks as these genes” and produce reprogrammed cells without genetic alterations, he says.(此文选自Science2007年刊)　　Order:
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答案
解析1. A　由文章首段F首句可知，本文主要是关于一项科学研究成果的说明文，首句即是文章的中心思想 首段后文将达这项研究成果的重要性。以文章逻辑结构可知，下文肯定是对该项重大发现的研究工作过程进行具体阐述。A中首句The work builds on a study是过渡句，承上启下，开始讲述本项研究工作的背景，故选A。2. C　由前文 “In June this year, Yamanaka and another group”可知，由两组科学家都做了该项研究并得出了相似结论the cells were truly pluripotent，可见研究面临着竞争。C首句Now the race to repeat the feat in human cells has ended in a tie: Two groups report today that…中的race 形象地点明两组竞争性的研究，Now，today等词与上文In June this year在时间上起到了很好的衔接作用，又讲到they havereprogrammed human skin cells into so-called induced pluripotent cells证实了上文研究得出的结论，与上文形成呼应，符合行文逻辑，故为本题答案。3. B　在上一段中作者分别介绍了Thomson和Yamanaka两个研究小组在Yamanaka小组原来的研究基础上都获得了同样的重大发现，根据行文思路，接下来应该介绍一下这两个研究小组获得发现的研究过程。B、E分别讲两组的研究，E主要讲的是Thomson小组的研究过程，但B以In the new work开头，然后再介绍Yamanaka小组的实验过程，In the new work起到过渡作用，并且是叙述Yamanaka小组在先前已经做过的实验基础上进行的下一步研究过程，才有后来两个小组的共同研究结果，相比之下，B与前文的语义衔接更为紧密，属于上下文关系，故B为正确答案。4. E　详细阐述了Thomson小组的实验过程，是完全从头开始的，E后文中Like Yamanaka’s group，as Yamanaka used, and two different genes，less than Yamanaka’s technique等词从分表明这是与上文Yamanaka的实验进行了对比，与B紧密衔接，形成了前后呼应的关系，故E该排在B后。5. G　前文通过分别叙述两组不同实验的重大发现，说明这些发现的重要性like an earthquake for both the science and politics of stem cell research，选项G在首句中就先对文章描述的科学重大发现予以肯定是promising，但both techniques share a downside指出这两种技术存在相同的弊端，承上启下，故为正确答案。
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