Which one of the following statements regarding haemoglobin is correct?

• A. Haemoglobin present in RBC can carry only oxygen but not carbon dioxide
• B. Haemoglobin of RBC can carry both oxygen and carbon dioxide
• C. Haemoglobin of RBC can carry only carbon dioxide
• D. Haemoglobin is only used for blood clotting and not for carrying gases.