You want to test the effects of water aerobics on resting heart rate. You decide to test two different levels of exercise (water aerobics for 30 minutes twice a week and water aerobics for 60 minutes once per week.) You randomly find a group of 60 subjects (30 men and 30 women) for this study. What is an appropriate design for this study?

A). Randomized block design

B). Completely randomized design

C). Matched pairs design