All of the following statements regarding biovailability of a drug are true except______________?

A. It is the proportion (fraction) of unchanged drug that reaches the systemic circulation
B. Biovailability of an orally administered drug can be calculated by comparing the area under cure (o-a) after oral and intravenous (IV) administration
C. Low oral biovailability always and necessarily mean poor absorption
D. Biovailability can be determined from plasma concentration or urinary excretion data