You are the lead researcher doing a study on the effects of vitamin C on gingival health. You randomly assign subjects with gingivitis into 2 groups. One group you administer high doses of vitamin C, the other gets a placebo. You then investigate the effect on their gingival health at regular 2 week intervals for 6 months. Is this an interventional or observational study? Select one: Q a. Interventional O b. Observational