Suppose that you want to perform a hypothesis test to compare the means of two populations, using a paired sample. For each part, decide whether you would use the paired t-test, the paired Wilcoxon signed-rank test, or neither of these tests, if preliminary data analyses of the sample of paired differences suggest that the distribution of the paired-difference variable is
a. Approximately normal.
b. Highly skewed; the sample size is 20.
c. Symmetric bimodal.