单选题 {{B}}Passage Three{{/B}}
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. "
单选题 Three years ago, researchers reported that cancer ______.
【正确答案】 A
【答案解析】[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。
单选题 Other scientists were skeptical of the report because ______.
【正确答案】 A
【答案解析】[解析] 本题是细节题。该题内容出现在文中第一段的中间部分。因为报告认为癌症是由单一基因造成的，故另一些科学家对如此简单的直接的过程需要几年甚至十几年的发展而感到怀疑，所以A选项是正确答案。B选项与文中内容不符，这不是科学家产生怀疑的根本原因，C选项不合题意，文中科学家已经宣称单个基因也可能引发癌症。D选项内容文中没有涉及。
单选题 The word "malignant" (line, 2 Para. 1 ) probably means ______.
【正确答案】 C
【答案解析】[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。
单选题 Cells injected with a single cancer gene ______.
【正确答案】 D
【答案解析】[解析] 本题是细节题。文中第二段讲，Each group found that it does in fact take more than a single gene to produce cancer in normal cells. 每一个实验小组都发现，产生癌细胞至少需要两种以上的基因。且本段中给出了一个试验小组的例证来阐明这个观点。可见单一的致癌基因会发生某些变化，但不会成为癌症，故A、B选项错误，C选项内容从文中无从得知。所以D选项是正确答案。
单选题 British scientists' demonstration implies that ______.
【正确答案】 B
【答案解析】[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。