Respiratory System Question????

From my current knowledge I believe the answer is B. I can't really give exact answers for why the others are not right, it just doesn't sound right. I do know thought that Oxygen binds to 4 Heme rings to cause oxygen saturation. When there is a lack of oxygen binding to hemoglobin it can cause a change of pigmentation. Iron is also in the heme group, but Fe does not bind to O2, O2 binds to heme, with Fe still being attached to heme.....Hope it helps.