To Become Bound to Haemoglobin for Transport in Mammals, Atmospheric

To become bound to haemoglobin for transport in mammals, atmospheric molecules of oxygen must cross ________.

A) one membrane-that of the lining in the lungs-and then bind directly to haemoglobin, a protein dissolved in the plasma of the blood
B) two membranes-in and out of the cell lining the lung-and then bind directly to haemoglobin, a protein dissolved in the plasma of the blood
C) four membranes-in and out of the cell lining the lung, in and out of the endothelial cell lining an alveolar capillary-and then bind directly to haemoglobin, a protein dissolved in the plasma of the blood
D) five membranes-in and out of the cell lining the lung, in and out of the endothelial cell lining an alveolar capillary, and into the red blood cell-to bind with haemoglobin