Final answer:
The higher the pH, the more easily oxygen combines with hemoglobin.
Step-by-step explanation:
The higher the pH, the more easily oxygen combines with hemoglobin.
When the pH is higher (more basic), the affinity of hemoglobin for oxygen increases, making it easier for oxygen to bind to hemoglobin. On the other hand, when the pH is lower (more acidic), the affinity of hemoglobin for oxygen decreases, making it harder for oxygen to bind to hemoglobin.
Therefore, the correct answer is A) pH; hemoglobin.