I guess I and III, but this onption is not included here.

I. if we write out the formula of mean, we can easily find that mean has to be 0

II. {-3,-1, 0,4} satisfies the condition, but the sum of the largest member and the smallest member of the set is 4-3=1

III. A set of something means in GMAT non repetitive list. So, the set has to contain positive and negative integers to have the mean=0. {0,0,0,0} - is not a set in GMAT.

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