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': 'Length of the sprue former in phosphate bonded investment material should be: \nSelect and explain. \nA. 6mm, B. 5mm, C. 4mm, D. 3mm', 'role': 'user'}, {'content': 'Answer: D \nExplanation: In general it should be 6 mm but if specifically mentioned for gypsum bonded length should be 6mm, while for phosphate bonded should be 3mm.', 'role': 'assistant'}]