The correct option is D RBCs
WBCs are white blood cells of the immune system, that are involved in defending the body against diseases.
Plasma is the liquid component of the blood that normally holds the blood cells.
RBCs are red blood cells, which contain hemoglobin. Hemoglobin is the iron-containing oxygen-transport metalloprotein. Hb in the blood carries oxygen from the respiratory organs to the rest of the body.
Platelets are blood cells, whose function is to stop bleeding.
Thus, the correct answer is option (C), 'RBCs'.