Correct option is C
Erythrocytes (RBCs : Red blood cells) help in circulation of blood. RBCs contain haemoglobin, a protein that gives blood its red colour and enables it to carry oxygen from the lungs and deliver it to all body tissues.
Oxygen is used by cells to produce energy that the body needs, leaving carbon dioxide as a waste product. RBCs also carry carbon dioxide away from the tissues and back to the lungs.