Which Molecules Are Respiratory Gases or Chemical Forms of Respiratory

Which molecules are respiratory gases or chemical forms of respiratory gases?
I. O₂
II. O₃
III. CO₂
IV. HCO₃^-
V. N₂

A) I, II, and III
B) I, II, III, and IV
C) I, III, and IV
D) I, III, and V