critical regions for the hypothesis test are summarized as follows; If the alternative hypothesis is in the form of H1 : µ1 ≠ µ2 then rejection region is z > zα/2 or z < – zα/2 If the alternative hypothesis is in the form of H1 : µ1 < µ2 then rejection region is z < – zα If the alternative hypothesis is in the form of H1 : µ1 > µ2 then rejection region is z > zα. Therefore, the correct answer is B.