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: Radiology
Principle used in radiotherapy is 
Select and explain. 
A. Cytoplasmic coagulation, B. Ionization of molecule, C. DNA damage, D. Necrosis of tissue
B: Ionization of molecule
Answer: B: Ionization of molecule 
Explanation: B i.e. ionization of molecule