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
Phosphate bonded investment is made carbon free 
Select and explain. 
A. To prevent brittleness of alloy., B. To produce smooth casting., C. To prevent staining  of ceramic., D. For easier divesting of investment.
A: To prevent brittleness of alloy.
Answer: A: To prevent brittleness of alloy. 
Explanation: None