For which one of the following situations would a Wilcoxon rank-sum (or Mann-Whitney) test be appropriate?

a) Comparing the ratings of a new product on a 5-point Likert scale by a panel of consumers to their ratings of a competitor's product on the same scale.

b) Comparing the sweetness of a diet drink (rated from 1 to 10) as judged by a panel of teenage tasters and a panel of adult tasters.

c) Judging whether the height of the water at high tide at a marina increases more or less consistently as the phase of the moon changes from new to full.

d) Testing whether the distributions of the ratings of a new distance learning course were the same as rated (on the usual 5-point Likert scale) by Freshmen, Sophomores, Juniors, and Seniors who had taken the course.

e) Estimating the association between the value of homes and their age in a community known to have a number of very expensive mansions.