Choice "A" is correct. Variables sampling is used to determine whether a given account balance is reasonable.
Choice "c" is incorrect. Attribute sampling is used to test the attributes, or characteristics, of each item in a sample. In this case, attribute sampling would be used to determine if proper procedures with respect to pricing were followed for each item in the sample.
Choice "b" is incorrect. Attribute sampling is used to test the attributes, or characteristics, of each item in a sample. In this case, attribute sampling would be used to determine if inventory was properly recorded for each item in the sample.
Choice "d" is incorrect. Attribute sampling is used to test the attributes, or characteristics, of each item in a sample. In this case, attribute sampling would be used to determine if discounts were properly applied to inventory for each item in the sample.