Which of the Following Scenarios Best Illustrates a Cohort-Sequential Design

Which of the following scenarios best illustrates a cohort-sequential design?

A) Don studies high school seniors' concerns about world events during their post-secondary experiences.He surveys the entire senior class state-wide.He surveys them again every year for eight years.
B) Melanie is conducting a survey for her thesis that examines administrative policies in middle schools that are intended to decrease bullying.After developing her survey and piloting the instrument with a small group,she then administers the instrument to a sample of 2300 middle-school administrators.
C) Jana wants to understand what predicts student success on the statewide standardized biology competency test.She administers the Biology Interest Survey (BIS) to all of her students at the start of the term and then categorizes students into two groups: those who have taken biology before and those who have not.She then administers an in-class exam at the end of the term.
D) Molly's study examines the benefits of exercise on weight loss.In one group she advocates exercise as well as a new diet program.In the comparison group she only presents the diet program.Those in the comparison group find out that some of Molly's clients are in an exercise program too,so they form an exercise group on their own.