A weakens the argument as it gives us reason to believe there is some alternative reason why one may wear tinted glasses other than that supposed by the argument.
B doesnt really do anything. It tells us how we should treat patients, but it does not tell us anything about ho likely it is that those who wear the glasses have the condition.
C weakens as it shows that we may be unable to generalize the results outside of Britain.
D does the same.
E weakens as it shows that we may not be able to generalize the results beyond the conditions studied.
