请帮忙解释一道逻辑题（11OG-48）

nicolechan28

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 people with normal or high

immune-system activity. The researcher concluded from this 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 systems.

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

D. Mental illness does not cause people’s immune-system activity to decrease.

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

答案是选D。请问为什么？

wycg

原文里有个因果关系,就是说因为免疫系统弱的人得分低(免疫系统强的人得分高),所以免疫系统强能阻止mental illness.

D说了一个原因就是"免疫系统弱的人得分低不是因为mental illness使人的免疫系统弱的",就是排除了一个能weaken原文的issue(把D取非就能weaken原文), 也可以说D就是assumption. 

nicolechan28

谢谢斑竹～～