A large proportion of oxygen is left unused in the human blood even after its uptake by the body tissues. This O2
(a) acts as a reserve during muscular exercise
(b) raise the pCO2 of blood to 75 mm of Hg.
(c) is enough to keep oxyhaemoglobin saturation at 96%
(d) helps in releasing more O2 to the epithelial tissues.
