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: Dental
[{'content': 'Greening refers to: \nSelect and explain. \nA. Greenish discolouration of porcelain due to escaping of silver vapours, B. Also known as wet strength of gypsum product, C. Observed in silica bonded investments due to drying of colloidal silica gel, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Discoloration\xa0of\xa0the\xa0porcelain\xa0near\xa0the\xa0cervical\xa0region\xa0of\xa0the metal-ceramic prosthesis has been reported to occur when a silver-containing alloy is used as the substrate.\xa0\nColor changes\xa0included\xa0green,\xa0yellow-green,\xa0yellow-orange,\xa0orange and brown hues.\xa0\nThis\xa0discoloration\xa0phenomenon\xa0has\xa0generally been called “greening.”\n\nRef: Phillip’s Science of Dental Materials ed 12 pg 380', 'role': 'assistant'}]