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': 'Thermal shrinkage in Phosphate bonded investment\noccurs due to release of \nSelect and explain. \nA. CO2, B. H2, C. NH3, D. Methane', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]