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
The X-ray collimators commonly used in dentistry include
the following, except 
Select and explain. 
A. Diaphragm collimator, B. Tubular collimator, C. Rectangular collimator, D. Square collimator
D: Square collimator
Answer: D: Square collimator 
Explanation: None