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
Length of the sprue former in phosphate bonded investment material should be: 
Select and explain. 
A. 6mm, B. 5mm, C. 4mm, D. 3mm
D: 3mm
Answer: D: 3mm 
Explanation: 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.