This is easy one !

Two premises. Avoid extreme choice and avoid choices which guarantee results. E.g. No, never etc

P1 :Left handed (LHP) personal suffer more frequently than do right-handed persons (RHP) from certain immune disorders (allergies)
P2 : LHP tend to have advantage over RH majority in activities such as mathematical reasoning

(A) Most people who suffer from allergies or other such immune disorders are left-handed rather than right-handed. >>> Y-> X. This is reverse of stimulus which says LHP have immune disorders/allergies. Wrong

(B) Most left-handed mathematicians suffer from some kind of allergy. >>> Extreme. Wrong

(C) There are proportionally more left-handers among people whose ability to reason mathematically is above average than there are among people with poor mathematical reasoning ability. >>> Lame so keep it. No contradictions.

(D) If a left-handed person suffers from an allergy, that person will probably be good at mathematics. >>> Y->X. Stimulus says that LHP have allergies. LHP tend to have good math reasoning. Does not mean allergies lead to good math reasoning. Wrong.

(E) There are proportionally more people who suffer from immune disorders such as allergies than there are people who are left-handed or people whose mathematical reasoning ability is unusually good. >>> Classical GMAT Comparison Trap. Stimulus doesn't even talk about this comparison. Wrong

C it is.
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Good one.. I fell for E

Was wavering between E and C.Fell for E finally....