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
Commonly used collimating device 
Select and explain. 
A. Aluminium filter, B. Lead diaphragm, C. Molybdenum cup, D. Tungsten filament
B: Lead diaphragm
Answer: B: Lead diaphragm 
Explanation: The collimating device often used is a lead diaphragm with a circular aperture for circular PIDs or a rectangular aperture for rectangular PIDs and the lead-lined PID. 
Frommer’s Radiology for Dental Professional, pg-22