GMAT Critical Reasoning (CR) | OG VR2 #7 Pls help

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 immunesystem
activity
...

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