This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
[{'content': 'The term physical half life is applicable to \nSelect and explain. \nA. Respiratory preparation, B. Prodrugs, C. Radioactive isotopes, D. Alkylating agents', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Physical half-life is defined as the period of time required to reduce the radioactivity level of a source to exactly one half its original value due solely to radioactive decay. The physical half-life is designated tphys or more commonly t1/2 . Refer 6/e p252', 'role': 'assistant'}]