This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
The term physical half–life is applicable to: 
Select and explain. 
A. Repository preparations, B. Prodrugs, C. Radioactive isotopes, D. Alkylating agents
C: Radioactive isotopes
Answer: C: Radioactive isotopes 
Explanation: None