Which fact suggests that most oxygen is transported from lungs to the tissues combined with haemoglobin rather than dissolved in blood plasma?

• A
  Oxygen carrying capacity of whole blood is much higher than that of plasma and oxygen content of blood leaving the lungs is greater than that of blood entering the lungs.
• B
  Haemoglobin can combine with oxygen.
• C
  Oxyhaemoglobin can dissociate into haemoglobin and oxygen.
• D
  Increase in carbon dioxide concentration decreases the oxygen affinity of haemoglobin.