17. Prоfessоr Rоcky Jаckson wаnts to determine whether soy protein powder cаn slow the aging process. So, he conducts a research study and assigns those with odd number birth year into one group and they consumed a non-soy protein powder mixed with milk. He assigns another group with even number birth year into another group and they consumed a soy protein powder mixed with milk. What type of research study is this?