Which of the following is one of the three main functions of the respiratory system?

The main functions of the respiratory system include the exchange of gases, which primarily involves the uptake of oxygen and the removal of carbon dioxide, a waste product of metabolism. Among the options provided, the removal of waste products of metabolism accurately captures a core function of the respiratory system by indicating its role in expelling carbon dioxide from the body. This process is vital for maintaining the body's acid-base balance and ensuring that tissues receive adequate oxygen while preventing the buildup of harmful metabolic byproducts.

Oxygen transportation is largely the role of the circulatory system, which carries oxygen absorbed in the lungs to the body’s tissues. Temperature regulation and fluid balance are also functions associated more closely with other systems in the body, such as the integumentary and renal systems, respectively. These clarifications help contextualize why the removal of waste products of metabolism is a fundamental function of the respiratory system.