曼哈顿的一道逻辑题，看了解释还是不懂为什么D不对。请大家帮我看看。

ranfly0089

Two genes, BRCA1 and BRCA2, are linked to hereditary breast cancer. Therefore, in order to decrease the annual number of mammogram tests administered across a population and to more accurately assess a woman's individual risk of breast cancer, all women should be tested for these genes.

Which of the following is an assumption on which the argument depends?

(A) Some of the women who are tested for the two genes will subsequently undergo mammograms on a less frequent basis than they used to.

(B) The majority of breast cancer patients have no family history of the disease.

(C) Researchers may have identified a third breast cancer gene that is linked with hereditary breast cancer.

(D) Women who have these genes have an 80 percent chance of getting breast cancer, while women who do not have these genes have only a 10 percent chance of getting breast cancer.

(E) The presence of BRCA1 and BRCA2 can explain up to 50 percent of hereditary cases.
A我知道是对的，可是后半段从“BUT does this have to be true"开始的解释我看不懂，If at least some women get tested and then get fewer Ms, then that would help to reduce \ the number of Ms. But does this HAVE to be true? Actually, I think so. It has to be the case that women who otherwise would've gotten Ms don't; otherwise, the number can't go down.

D 的解释我也看不懂，I f that's true, then it does sound like knowing whether you have the gene would help more \ accurately assess your risk. Does this HAVE to be true? Not with those specific numbers, actually. Tricky. Maybe it's 70 percent or 90 percent instead of 80%; the message is still the same.

求大牛指教！

拔萝卜的船长

前提说有某两个基因的女士更容易得癌症
这道题目的结论是为了减少MS test和精确测量风险，女士应该去检测这两个基因
A 检测了这两个基因后 女士进行MS test的频率会降低，从而达到了减少test风险的目的。那个后半句的解释是说那些本来要去MS test的女士不去了it has to be the case that women who otherwise would've gotten Ms don't，注意don't.所以使得number 下降了

D说有这两个基因的女士有80%会得癌症 没有这两个基因的只有10%的概率会得。注意这是假设题。是结论成立的前提。那个解释是在说，这个条件并不能作为一个结论成立所必需的，如果我说概率不是80%，是70%或者90%，那也不能削弱结论呀 所以取反削弱失败，并不能作为一个前提

拔萝卜的船长

两个楼主疑惑的地方应该都是在取反削弱上 A 也是说假如取反 number不下降 那结论就被削弱了.....我逻辑也做得不好 个人见解 仅供参考哈

nfnf

看到50%，80%我自动把这些选项排除了。。。因为这是assumption题目，假设是必须发生的事情，你咋知道准确到那么具体的数字的。。。

nfnf

而且这是典型的supporter类型的assumption题型，所以我上来就找带mammogram的答案。。。作为桥梁。。。

xiaoxuexiaoda

拔萝卜的船长 发表于 2015-7-26 15:02
前提说有某两个基因的女士更容易得癌症
这道题目的结论是为了减少MS test和精确测量风险，女士应该去检测这 ...

和80%无关吧？即使是70%、90%表达的意思都一样啊。解答中也写道：
If that's true, then it does sound like knowing whether you have the gene would help more accurately  assess your risk. Does this have to be true? Not with those specific numbers, actually. Tricky. Maybe it's  70% or 90% instead of 80%; the message is still the same.