All of the following statements regarding bioavailability of a drug are true except:

• A. Bioavailability of an orally administered drug can be calculated by comparing the Area Under Curve (o-alpha) after oral and intravenous (IV) administration
• B. It is the proportion (fraction) of unchanged drug that reaches the systemic circulation
• C. Bioavailability can be determined from plasma concentration or urinary excretion data
• D. Low oral bioavailability always and necessarily mean poor absorption