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': 'A 50 year old male patient complains of reduced mouth opening. Patient gives h/o RTA 1 week back. A panoramic X-ray was taken using an intensifying screen containing gadolinium and lanthanum. On interaction with X-rays, the contents of this intensifying screen emits: \nSelect and explain. \nA. Red light, B. Green light, C. Blue light, D. Yellow light', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Contemporary intensifying screens used in extraoral radiography\xa0use the rare earth elements gadolinium and lanthanum. These rare earth phosphors emit green light on interaction with\xa0X-rays.\xa0 Compared\xa0with\xa0the\xa0older\xa0calcium tungstate\xa0screens,\xa0rare\xa0earth\xa0screens\xa0decrease patient exposure\xa0by\xa055%\xa0in\xa0panoramic and cephalometric radiography.\nWhite and Pharoah, Oral radiology, ed 7th, pg-34', 'role': 'assistant'}]