There are three elements of this stimulus. Traumatic events, PTSD, and the hormone cortisol.
The premises established a correlation between PTSD, Traumatic events, and the hormone cortisol, but in the most extreme case, we cannot deduce anything from the mere correlation.
The author then concludes that Traumatic events can affect the hormone cortisol level, which is an implausible inference.
I can understand up to this point, but I don't know why B can weaken the argument as reverse causality.
B says high cortisol can help prevent PTSD.
First, I think there is still the possibility that Traumatic events cause a higher level of cortisol to prevent PTSD which strengthens the argument. TE
HC
no PTSD
Second, a reverse causality should be the one between cortisol level and Traumatic events rather than PTSD, like higher cortisol helps one avoid facing traumatic events.
I know that a weakened question does not need to overturn the argument, but I don't feel answer B weakens the argument in anyways.
I also like to use similar but simple cases to understand the difficult questions. I come up with a stimulus of my own. Suppose that a person who has got COVID but who didn't die has a higher level of antibody than those who didn't suffer from COVID. I conclude that COVID can affect antibody levels. (To be honest, I don't feel anything wrong with this stimulus, as I do with the original stimulus.)
Now, if I provide an answer saying that producing more antibodies helps prevent death, would you feel it is a weakening answer by reverse the causality?