Answer:
(A). hemoglobin
Step-by-step explanation:
Hemoglobin is iron-containing protein, present in RBCs (red blood cells) of nearly all vertebrates and some invertebrates. It is made up of four globular protein units.
The main function of hemoglobin is to transport oxygen to the different parts of the body. The oxygen is requires by the body cells to perform cellular respiration that generates energy in the form of ATP molecules.
Thus, the correct answer is option A.