[求助]请教一道逻辑推理题（假设） - ChaseDream

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 system.
(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 in medical treatment

答案是 D
能否解释一下为什么选D？十分感激！！！！

題目是說:低免疫系統level的人會得到比高免疫或正常免疫系統的人還要高分數的mental health test

B The similarity of mental disease and physical illness cannot draw a conclusion that the immune-system could protect them both.

D The best answer,makes it clear that the low immune system is not caused by the mental illness and thus clarifies the roles played by immune system and mental illness: the mental illness is not the reason of low immune system,so supports the conclusion.