Muscles move body parts by contracting and then relaxing. Muscles can pull bones, but they can't push them back to the original position. The nervous system tells the muscles to contract, but since you can only choose two, I would say muscles and bones. Without the bones, there would be nothing to move.
<em>I think that the two structures are muscle and the nervous system.</em>
<em>The reason I believe this is because in order to move we need to have control over our muscles and the nerves inside them that cause them to react to the commands our brains perform. Once both aspects are put together we are capable of moving our bodies.</em>
My answer would be to make sure to include the F.I.T.T principle (Frequency, Intensity, Time, and Type). I am not completely sure if it is correct so correct me if I am incorrect.
Explanation: The Paleolithic diet, Paleo diet, caveman diet, or stone-age diet is a modern fad diet requiring the sole or predominant eating of foods presumed to have been available to humans during the Paleolithic era.
