What Parameter Is Considered to Be the Most Accurate and Reliable

What parameter is considered to be the most accurate and reliable measure of oxygenation efficiency?

A) PaO₂/FIO₂ ratio
B) P(A - a) O₂/PaO₂ ratio
C) $\dot { \mathrm { Q } } _ { s } / \dot { \mathrm { Q } } _ { t }$
D) PaO₂/SaO₂ ratio