I think it's D. The researcher is saying that since mental illness and low immune system activity tend to occur together, it must be that mental illness is the result of the low immune system.

However, it could easily be that the causation is in the opposite direction and the low immune system activity is caused by the mental illness. But, for his conclusion to be valid, the researcher must assume that this is not the case.

I would think its A, but not 100% sure.

Another vote for D.

B is a close one as it seems to bridge the gap (or comparison) between
mental illness and physical disease. However, the conclusion is better
boosted by D.

Yeah D is the right answer.

FYI below is the explanation:

The researcher concludes from the association of low immune-system activity with low mental-health sores that, in effect, immune system activity can inhibit mental illness. If, 80
contrary to D, mental illness can depress immune-system activity, the association mentioned does not support the researcher’s conclusion. So D must be assumed. Normal immune-system activity could protect against mental illness without high-immune system activity offering increased protection or prevention, contrary to what A and C state, so neither
of A and C is assumed. The conclusion does not depend on there being a similarity between mental and physical illness or a difference in treatments, so B and E are not assumed.


I feel the answer is very indirect as the examinee has to think other way round in the way what are the effects of mental illness on immune systems instead of immune systems ability to prevent mental illness. What a crappy question!!!
i wish such quesions do not appear while i try my fate

POE works better in this question it leads to only D

hey rocky .. wat is POE ?

Process
Of
Elimination

I like explanation for D