Answer:
The correct answer would be C) respiratory system.
Respiratory system is made up of set of organs which help in taking in oxygen and expelling out carbon dioxide from the body.
In humans, it is composed of nose, pharynx, larynx, trachea, bronchi, pair of lungs, and diaphragm.
Alveoli (in lungs) are the site of gaseous exchange where oxygen is exchange with carbon dioxide.
Carbon dioxide is the toxic waste product of cellular respiration. Circulatory system helps in transporting CO₂ from cells to the alveolar site where it is exchanged with oxygen and excreted out as a part of exhaled air.