What is the primary function of the cardiovascular system during exercise?

The primary function of the cardiovascular system during exercise is to supply oxygen-rich blood to working muscles and remove waste products. During physical activity, the demand for oxygen increases as muscles work harder, leading to an increased heart rate and blood flow. This process ensures that muscles receive the necessary oxygen and nutrients to perform optimally while simultaneously enabling the removal of metabolic waste products, such as carbon dioxide and lactic acid, which can accumulate and lead to fatigue if not cleared efficiently.

While increasing muscle size and strength, regulating body temperature, and enhancing flexibility are important aspects of physical training and exercise physiology, they do not represent the primary function of the cardiovascular system specifically. The cardiovascular system's critical role during exercise is focused on oxygen transport and waste removal, making choice A the most accurate description of its primary function.