I believe it would be Heat Radiation
Although now it causes more harm than good because it doesn't really have a purpose, it is believed it once was used for humans to digest bone.
I would say keep the soil from eroding and doesn't let it get dried out so fast.
The answer is cotton. It is natural because it is grown and easily woven in to clothes :)
Think it's C since joints connects two bones together and marrow is inside bones.
