For oxygen to become bound to hemoglobin for transport in the blood, which of the following would be true?

A. 2 membranes must be crossed, in and out of the cell lining the lung and then bind directly to the hemoglobin

B. 4 membranes, in and our of the cell lining the lungs, in and out of the endothelial cell lining the alveolar capillary, and then bind directly to hemogloblin

C. 5 membranes – in and out of the cell lining the lung, in and out of the endothelial cell lining the alveolar capillary and into the RBC to bind to hemoglobin