The red color of the blood is due to ?
 

The red color of the blood is due to hemoglobin.

Blood has four main components that are RBC, WBC, Plasma, and platelets. Red blood cells consist of a molecule called hemoglobin. The hemoglobin is made up of four protein chains that each bind to additional ring-shaped chemical structure called heme. Our red blood cells are red because of the heme groups in hemoglobin. It binds with oxygen and carbon dioxide in order to transport them. 

Hence the correct answer is option A.