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': 'Penny test is done to detect: \nSelect and explain. \nA. Solution contamination, B. Defect in exposure, C. Unsafe illumination, D. Density of water', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Test\xa0for Checking Unsafe Illumination:\nFilm fogging can occur due to:\n\nUse of inappropriate safelight filters.\nExcessive exposure to safelight filters.\nStray light.\nCoin test/Penny test (A and B) is a test to evaluate for fogging caused by inappropriate safe lighting conditions.\n\t\nShut all lights and put on the safelights.\nOpen the unexposed film packet and place the base film in the area where films are usually unwrapped.\nPlace a coin on the film and leave it in this position for approximately the time required to unwrap and mount a full mouth set of radiographs, usually 5 min.', 'role': 'assistant'}]