A. Regulation of blood pressure: Carbon dioxide levels influence vascular tone indirectly, but blood pressure is primarily regulated by cardiac output, blood volume, and peripheral resistance. CO₂ production does not have a direct regulatory role in maintaining systemic arterial pressure. B. Regulation of pH: Carbon dioxide combines with water to form carbonic acid, which dissociates into hydrogen ions and bicarbonate. This relationship directly links CO₂ production to acid–base balance, making CO₂ a key determinant of blood pH through respiratory compensation. C. Regulation of body temperature: Temperature regulation involves metabolic heat production, sweating, and vasomotor changes. While CO₂ is a byproduct of metabolism, its production does not directly regulate body temperature. D. The synthesis of vasodilators: Vasodilators such as nitric oxide and prostaglandins are synthesized by endothelial and other cells. Their production is not directly dependent on the respiratory generation of CO₂, although CO₂ may influence vascular tone secondarily. E. Aids in defecation: Defecation is controlled by the enteric nervous system, abdominal pressure, and sphincter relaxation. CO₂ production has no functional role in initiating or supporting this process.