Rachael Has Been Hired by Mane, a Fitness Company, to See

Rachael has been hired by Mane, a fitness company, to see if their new fitness program is an effective method of reducing weight. She recruits 500 overweight people between the ages of 45-60 and randomly assigns them two groups. Group A consists of people who take part in Mane's fitness program for 5 hours a week, while group B consists of people who will undertake cardio and weight training, also 5 times a week. Both groups are instructed to maintain a balanced diet during the course of the experiment. After 3 months, Rachael finds that group A members have lost 10 percent of body fat, while group B members have lost 3 percent of body fat.
The research category that best fits this study is

A) randomized controlled experiment.
B) prospective observational study.
C) retrospective observational study.