2. 外语
  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

admin2012-02-27  20
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. "
Three years ago, researchers reported that cancer ______.
选项 A、was caused by normal cells
B、sometimes resulted from internal actions of the victim’s own body
C、was a hereditary disease
D、was a form of malignancy
答案A
解析 本题是细节题。该题内容出现在文中第一段。Three years ago，researchers announced the discovery of human genes that were capable of turning ordinary cells into malignant ones. 3年前，研究者们发现人类的基因能够使正常的细胞转变成恶性细胞。所以A选项是正确答案。B选项答案过于宽泛，而且文中没有提到癌症是由患者体内活动引起的。C选项内容文中没有提到。D选项针对malignant单词设置干扰项，但这并不是引起癌症的真正原因。
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