The answer is mitochondria
I would say the last option, the tilt of the axis/ rotation of the earth. Sorry if this is late, it says you asked a week ago. Hope this helps
You would expect an earthworm to have no exoskeleton because as you see it is very flexible and soft. Organisms with such have body parts that are divided and an earthworm do not have any visible parts on them also having an exoskeleton would not allow an organism to move like an earthworm does.
The principle underlying this change is called progression. This principle tells us that when your fitness level improves, your body has adjusted to your regular routine; thus, you will feel less sore than when you started the squats three weeks ago. During this time, your muscles have developed<span> and your body has adopted to the stress brought about by your exercise. </span>
