The cardiorespiratory system includes the following parts of the body heart, lungs, and liver
heart, lungs, and liver

heart, lungs, blood, arteries, veins, and muscle cells
heart, lungs, blood, arteries, veins, and muscle cells

heart, lungs, and blood
heart, lungs, and blood

lungs, arteries, and muscle cells
lungs, arteries, and muscle cells

I think it might be heart, lungs, blood, arteries, veins, and muscle cells

Explanation:

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.