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  3. Three years ago, researchers announced the discovery of human genes that were capable of turning ordinary cells into malignant o

Three years ago, researchers announced the discovery of human genes that were capable of turning ordinary cells into malignant o

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问题     Three years ago, researchers announced the discovery of human genes that were capable of turning ordinary cells into malignant ones. The news met with some skepticism. Experts asked how a single gene could cause such a dramatic change. Why does cancer take years or even decades to develop if it is caused by such a simple and direct process? In last week’s issue of the, three research teams answered those questions by setting forth a new model for understanding the role of oncogenes in cancer.
    Each group found that it does in fact take more than a single gene to produce cancer in normal cells. Teams at M. I. T and Cold Spring Harbor Laboratory on Long Island, N. Y. , reported that they could induce cancer in normal rat cells only by inserting at least two types of oncogene into the cells. "A single oncogene produced some changes, but not cancer," explained molecular biologist Robert Weinberg of MIT. It took two genes acting cooperatively to produce a tumor. In other cases, it might take three or more.
    A British team confirmed the multistep cancer scenario by showing that a particular oncogene caused a tumor in hamster cells only if they had first been exposed to a carcinogenic chemical. The chemical alone and the oncogene alone did not cause cancer, both were necessary. While the discovery has no immediate implication for treatment of cancer, it helps explain why the disease develops slowly and why its incidence rises with age. "Even if one part of the process occurs," says Weinberg, "you might not have the second step for another 20 years. "
British scientists’ demonstration implies that ______.
选项 A、single cancer genes are harmless
B、the development of cancer is a complex process
C、a carcinogenic chemical is required for cancer to develop
D、cancer genes can cause cancer only in conjunction with a carcinogen
答案B
解析 本题是推理题。A选项不是暗示的，而且在第一段中讲到单个的恶性细胞能够产生巨变，与文章内容不符。在B选项中谈到了仓鼠的细胞只有在感染了致癌化学物质时，一种致癌基因才会引起肿瘤。可见这也不是推知，而且与文中内容不符。D选项错误，因为文中谈到了只是一种致癌基因和一种化学物质都无法产生癌细胞，也与原文不符。所以只有B选项是正确答案。因为文中提到研究者们的新发现，但是引发了不少怀疑的声音。许多研究小组认为，单个基因无法产生癌变，而是需要更多的化学物质和基因相互结合才会产生癌细胞，可见这是一个非常复杂的过程。所以B选项是正确答案。
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