Suppose that you want to perform a hypothesis test based on independent random samples to compare the means of two populations. For each part, decide whether you would use the pooled t-test, the nonpooled t-test, the Mann–Whitney test, or none of these tests if preliminary data analyses of the samples suggest that the two distributions of the variable under consideration are

a. normal but do not have the same shape.

b. not normal but have the same shape.

c. not normal and do not have the same shape; both sample sizes are large.