Your answer is C surfing because when you surf you have to have a surfboard, also you need a strap that will hold you leg also its not B because walking requires nothing except you its not D because yoga just requires a mat and your "mind" and when you came down to A, and C I choose C because A requires machinery but you don't have to buy machinery you can do things like push-ups, or other things that can build up your muscular strength and endurance. Your answer is C.
