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 and have the same shape.

b. not normal and do not have the same shape; one of the sample sizes is large and the other is small.

c. different, one being normal and the other not; both sample sizes are large.