The partial pressures (in `` mm Hg `` ) of oxygen `` \left( O _{2}\right) `` and carbon dioxide `` \left( CO _{2}\right) `` at alveoli (the site of diffusion) are:
(A) `` pO _{2}=104 `` and `` pCO _{2}=40 ``
(B) `` pO _{2}=40 `` and `` pCO _{2}=45 ``
(C) `` pO _{2}=95 `` and `` pCO _{2}=40 ``
(D) `` pO _{2}=159 `` and `` pCO _{2}=0.3 ``