【简答题】In cells and tissues, __________ and _________ buffer systems maintain intracellular and extracellular fluids at their optimum pH, which is usually close to 7.
【简答题】The economically optimum stand management plan for an owner is that which maximizes the net present value or willingness to pay for bare land just before ______.
【简答题】In cells and tissues, _______ and _________ buffer systems maintain intracellular and extracellular fluids at their optimum (physiological) pH at 7.