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
The function of a sprue is to: 
Select and explain. 
A. Form an opening for molten metal to enter the mold, B. Help polish cast restorations, C. Eliminate air bubbles on the wax pattern, D. Reproduce fine detail
A: Form an opening for molten metal to enter the mold
Answer: A: Form an opening for molten metal to enter the mold 
Explanation: None