Sara was given an assignment to prove that there are different levels of complexity in the human body. Her teacher told her to go from least complex to most complex.
What is the order in which she should use to prove this

And the 1 points are for this 20 if i get all 3 of them correctly i will give you brainliest and if you only get all 3 i will give you brainliest including a and the rating will be 5 and if you get those i will give you 20 points