我选C, support作者: cranberry 时间: 2003-9-12 13:04
请帖出原题作者: fyhllj 时间: 2003-9-12 13:11
4. Although exposure to asbestos is the primary cause of mesothelioma, a slow-developing cancer, researchers believe that infection by the SV40 virus is a contributing cause, since in the United States 60 percent of tissue samples from mesotheliomas, but none from healthy tissue, contain SV40. SV40 is a monkey virus; however, in 1960 some polio vaccine was contaminated with the virus. Researchers hypothesize that this vaccine was the source of the virus found in mesotheliomas decades later. Which of the following, if true, most strongly supports the researchers’ hypothesis? A. SV40 is widely used as a research tool in cancer laboratories. B. Changes in the technique of manufacturing the vaccine now prevent contamination with SV40. C. Recently discovered samples of the vaccine dating from 1960 still show traces of the virus. D. In a small percentage of cases of mesothelioma, there is no history of exposure to asbestos. E. In Finland, where the polio vaccine was never contaminated, samples from mesotheliomas do not contain SV40. 作者: fyhllj 时间: 2003-9-12 13:18
E is correct answer. 对其取非In Finland, where the polio vaccine was never contaminated, samples from mesotheliomas do (not) contain SV40. 则Researchers hypothesize that this vaccine was the source of the virus found in mesotheliomas decades later.不成立。 支持题有时也可使用取非法。
Hope it is helpful.
作者: cranberry 时间: 2003-9-12 14:06
先确定假说的范围，即是最后一句，重点是那些疫苗是源头，而不是别的。要证明那些疫苗是源头的话，必须提出一个证据，即没有那些疫苗的话，便不会有后来发现的事实，E是很好用的例子啊。我们不要混淆，假说本身没讨论致病的机理问题。c 说的是1960年的疫苗仍有病毒，但这说明不了它是源头，可能还有别的感染源啊。肯定是一种支持，但绝对不是最强的支持。作者: qiqi_cola 时间: 2003-9-12 21:30
同意4楼的。Researchers hypothesize that this vaccine was the source of the virus found in mesotheliomas decades later. 这道题关键在这句话， VACCINE----》 VIRUS IN MSOTHELIOMAS，
答案E，是这个结论的逆否命题。作者: cooperqi 时间: 2003-9-14 14:00
i see now. thx