A manufacturer of pens has hired an advertising agency to develop an advertising campaign for the upcoming holiday season. To prepare for this project, the research director decides to initiate a study of the effect of advertising on product perception. An experiment is designed to compare five different advertisements. Advertisement A greatly undersells the pen's characteristics. Advertisement B slightly undersells the pen's characteristics. Advertisement C slightly oversells the pen's characteristics. Advertisement D greatly oversells the pen's characteristics. Advertisement E attempts to correctly state the pen's characteristics. A sample of 30 adult respondents, taken from a larger focus group, is randomly assigned to the five advertisements (so that there are 6 respondents to each advertisement). After reading the advertisement and developing a sense of "product expectation," all respondents unknowingly receive the same pen to evaluate. The respondents are permitted to test the pen and the plausibility of the advertising copy. The respondents are then asked to rate the pen from 1 to 7 (lowest to highest) on the product characteristic scales of appearance, durability, and writing performance. The combined scores of three ratings (appearance, durability, and writing performance) for the 30 respondents, stored in Pen, are as follows:

a. At the 0.05 level of significance, is there evidence of a difference in the mean rating of the pens following exposure to five advertisements?
b. If appropriate, determine which advertisements differ in mean ratings.
c. At the 0.05 level of significance, is there evidence of a difference in the variation in ratings among the five advertisements?
d. Which advertisement(s) should you use, and which advertisement(s) should you avoid? Explain.