Concept:Oxygen is carried in the blood by a red pigment found inside red blood cells.Explanation:Plasma is the liquid part of blood, not a pigment.Erythrocytes are red blood cells that transport oxygen, but they are cells, not pigments.Haemoglobin is the red pigment inside red blood cells.It picks up oxygen in the lungs and becomes oxyhaemoglobin.Oxyhaemoglobin releases oxygen to body tissues, but the actual oxygen-carrying pigment is haemoglobin.Answer:B. haemoglobin