During the late 1980s and the early 1990s the Pepsi Challenge was in full swing. During the challenge, participants were asked to taste cola from both Coke and Pepsi. Once they had tasted both drinks, the participants were asked to report which tasted better. The results indicated that participants found Pepsi products tasted better. What kind of research design was used?

a. between subjects design;
b. concurrent measures design;
c. mixed subjects design;
d. multigroup design.