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
[{'content': "Which of the following statements best describes `Background Radiation' – \nSelect and explain. \nA. Radiation in the background of nuclear reactors, B. Radiation in the backgroung during radiological investigations, C. Radiation present constantly from natural sources, D. Radiation from nuclear fall out", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Background Radiation refers to radiation exposure received from natural sources such as extraterrestrial cosmic rays, terrestrial sources and from radionucleotides present within the body. Background radiation is ubiquitously distributed and received constantly.', 'role': 'assistant'}]