Identify the Study as an Observational Study or a Designed

Identify the study as an observational study or a designed experiment.
-A researcher wished to assess the importance of exercise in weight-loss programs. 412 people, all considered to be at least 20 pounds overweight, volunteered to participate in a study. The
Participants were randomly assigned to one of two groups. Over a two-month period, the first Group followed a particular diet but were instructed to perform no exercise other than walking. The second group followed the same diet but also performed aerobic exercise for one hour each Day. At the end of the two months, the weight loss of each participant was recorded. The average Weight loss was calculated for each group and it was found that the average weight loss for the Second group was significantly greater than the average weight loss for the first group.

A) Designed experiment
B) Observational study