19. The human respiratory system is a series of organs responsible for taking in oxygen and expelling carbon dioxide.
20. nose, mouth, pharynx, larynx, trachea, bronchi, and lungs
21. Can't answer
22.Digestion is the breakdown of food into small molecules, which are then absorbed into the body.
23. mouth, esophagus, stomach, small intestine, large intestine
24. Don't Know