Three years ago, researchers announced the discovery of human genes that wer

游客2025-03-24 4

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. " [br] The word "malignant" (line, 2 Para. 1 ) probably means ______.

选项 A、contagious
B、chronic
C、virulent
D、injured

答案 C

解析本题是词汇理解题。出现在文中第一句。科学家宣称了一个结果，引发了争议。结合整段的理解，其他科学家对这个结果怀疑的根据是为什么一个基因能够产生巨变，而在这种简单直接的情况下癌症为什么会有几年甚至几十年的潜伏期。说明基因从一个健康的细胞转变为了一个“有害的，恶性的”其他细胞。所以C选项是正确答案。contagious意为“传染的”；chronic意为“慢性的”；injured意为“有损害的”。均不符合题意。

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