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
Which of the following statements best describes 'Background Radiation' 
Select and explain. 
A. Radiation in the background of nuclear reactors, B. Radiation in the background during radiological investigations, C. Radiation present constantly from natural sources, D. Radiation from nuclear fall out
C: Radiation present constantly from natural sources
Answer: C: Radiation present constantly from natural sources 
Explanation: C i.e. Radiation present constantly from natural sources Back ground radiation is a low level, wide spread (ubiquitous), constantly present radiation from natural sources that is usually not detrimental to lifeQ.