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
Hounsfield Units depends on: 
Select and explain. 
A. Electron density, B. Mass density, C. Effective atomic number, D. Attenuation coefficient
D: Attenuation coefficient
Answer: D: Attenuation coefficient 
Explanation: D i.e. Attenuation coefficient