Upon the entry of carbon dioxide in the red blood cells, H+ionsare formed at a very rapid rate, and yet the blood does not turn acid because (a) H+ ions are rapidly exchanged at the expense of HCO3-ions (b) H+ ions are rapidly removed and excreted in the urine (c) H+ ions are buffered by proteins of haemoglobin and plasma (d) H+ ions are buffered by proteins of haemoglobin and proteins and phosphates of plasma