By components do you mean organs? If so...
1. Brain - gives demands ands orders to all of the body to function properly
2. Heart - pumps blood, and keeps the organism receiving the blood alive
3. Skin - protects the tissue from UV Rays that may be harmful
D because it helps to get the thing that there choking on out of them
B. most exercise machines require spotters for safe operation.
Your answer is C.........