The pH of human blood is maintained within a narrow range, typically 7.35 to 7.45, which is slightly alkaline. Option C, 7.4, falls within this normal range and is often cited as the average blood pH. Normal blood pH is slightly alkaline, maintained tightly between 7.35 and 7.45. Maintaining blood pH within this narrow range is crucial for various physiological processes, such as enzyme activity and oxygen transport. Deviations from this range can lead to serious health problems (acidosis below 7.35 or alkalosis above 7.45).