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
Conventional unit of Exposure is: 
Select and explain. 
A. C/Kg, B. Air Kerma, C. Roentgen, D. Rad
C: Roentgen
Answer: C: Roentgen 
Explanation: Units (Dosimetry) (Very important):