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 would be most seriously weakened if it were true that

Question

Examsnet · Accepted Answer

Correct Answer is :  high levels of stress first cause mental illness and then cause decreased immune-systemactivity in normal individuals

GMAT Verbal Reasoning Practice Test 4