This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pharmacology, Subject name: Pharmacology
[{'content': 'What does the term "bioavailability" mean? \nSelect and explain. \nA. Plasma protein binding degree of substance, B. Permeability through the brain-blood barrier, C. Fraction of an uncharged drug reaching the systemic circulation following any route administration, D. Amount of a substance in urine relative to the initial doze', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Bioavailability is defined as the fraction of unchanged drug reaching the systemic circulation following administration by any routeBasic and clinical pharmacology Katzung 13th edition pg 47', 'role': 'assistant'}]