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 ilness as well as against physical disease.

The researcher's conclusion depends on which of the following assumption??

答案是 D Mental illness does not cause people's immune-system activity to decrease.

题目都说 low levels of immune-system activity 会造成 lower score on tests of mental health，为何结论还会建立在

"Mental illness does not cause people's immune-system activity to decrease" 的假設上？？

Mental illness does not cause people's immune-system activity to decrease" 的假設上？？"

原题只是说tend to,两种现象并存。

Because if something is a cause of another, it can't be a result of another.

'coz both kinds of people have the same chance to get mental illness, but the people having higher level of immune system activity tend to get over it better than the people with lower level of that.

which is based on the assumption: Mental illness does not cause people's immune-system activity to decrease.

If mental illness does cut down the immune-system activity as AIDS does, they will score the same.