48. A researcher discovered that people who have low levels of immune-system activity tend to score much lower on tests of mental health than do poeple with normal or high immune-system activity. The researcher concluded form thsi experiment that the immune system protects against mental illness as well as against physical disease.
The researcher's conclusion depends on which of the following assumptions?

(A)High immune-system activity protects against mental illness better than normal immune-system activity does.

(B)Mental illness is similar to physical disease in its effects on body system.

(C)People with high immune-system activity cannot develop mental illness.

(D)Mental illness does not cause poeple's immune-system activity to decrease.

(E)Psychological treatment of mental illness is not as effective as is medical treatment.

有的朋友说Ｄ正确是因为它是原题的逆否命题。可是逆否命题的定义是　非Ｂ－＞非Ａ　

这样的话，原题的逆否应该是： if no mental illness, immune system activity will not decrease..

这句话和D等价么？我觉得不等价阿。。。

哪位逻辑高人指点一下。。。。

另外请帮忙印证： 非B->非A  等价于  非(B->A)   么？

顶一下

我还有个问题,原文说low levels of immune-system activity  得分底 结论说,免疫系统能抵抗精神疾病,也能抵抗身体疾病

我觉得原文论据中没有提身体疾病,而结论中给出个身体疾病,那假设应该是把身体疾病和结论联系起来,所以我选了b,

请高人指点一下

发现：免疫系统低--精神状况差
结论：免疫系统作用于精神，作用于身体
assumption: 精神状态不作用与免疫系统

这道题目的意思是，当2个现象同时发生的时候，A未必是造成B的原因，很有可能B才是造成A的原因。

请指教。

 D

not+weaken

这个题目的类型你一定不会陌生的！！你也做过大全吧～这类题目经常先列出两个事物，Ａ和Ｂ，然后就说Ａ－＞Ｂ．经常会问的类型就是削弱，那就是Ｂ－＞Ａ．就是所谓的因果倒置．．

其实Ｄ就是用了非Ｂ－＞Ａ的方法来解释了只有Ａ－＞Ｂ的．希望我的解答你能明白啊！！

D选项取非后是因果倒置

Argument:  low levels of immune-system activity ---> low mental health

D选项：low mental health ---> low levels of immune-system activity