Answer:
Gravity?
Explanation:
Or it could be a non contact force.
Think it's C since joints connects two bones together and marrow is inside bones.
Okay, this has to be in your own words, but I will tell you this. Natural Selection is living organisms that have adapted to the environment which surrounds them leading the the producing of offspring. Example, bugs are eaten by frogs and frogs are eaten by snakes and snakes are eaten by birds.
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Awnser is d hope this helps