Option D is the correct answer. Demographics of a population are different aspects of their characteristics, such as age.
The main function of the <u>respiratory system is breathing</u>, a process that is also referred to as respiration. This
process allows the body to bring in oxygen and expel (get rid of) carbon dioxide. During respiration, oxygen travels
through the bloodstream and carbon dioxide is carried away.
Breathing air into your body is also necessary for <u>speaking</u>.
