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
Isotope which is replacing radium is: 
Select and explain. 
A. Cesium, B. Iridium, C. Gold, D. Californium
B: Iridium
Answer: B: Iridium 
Explanation: Ans. Iridium