Twenty customers are randomly chosen, and each is given a sample of Nut Butter ice cream to taste. The customers rank the taste of the ice cream on a 10-point scale. Each is then given a sample of Chewy Gooey ice cream to taste and rank on a 10-point scale. Based on the 20 customers' ratings of each flavor, the research analyst conducting the survey wishes to determine if one flavor is preferred over the other. Which nonparametric test would you use to determine if there is a difference in the ratings?

a.Wald-Wolfowitz one-sample runs test

b.Kruskal-Wallis test

c.Wilcoxon signed-rank test

d.Wilcoxon rank sum (Mann-Whitney) test