In each case below, a study is described to determine whether exercise helps increase certain mood enhancing chemicals in the brain. Indicate whether each describes an experiment or an observational study. State a reason for your choice. (i) (ii) We contact a random sample of 100 people and record how much each person exercises and also measure the chemicals in the brain of each person. Using a random sample of 100 people, we randomly assign half of them to participate in a regular exercise program for six weeks while the other half makes no changes. At the end of the time period, we measure the brain chemical of each person.