Nora is interested in differences in amount of content retained from a lecture based on time of class. She compares her two sections. Section A meets at 8 am and Section B meets at 2 pm. She tests students in both sections, unannounced, on content that she taught two weeks ago.
Which of the following designs is Nora best illustrating?

a. One-group posttest-only design
b. One group pretest-posttest design
c. Posttest only control group design
d. Posttest-only design with nonequivalent groups