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
Incomplete casting is the result of 
Select and explain. 
A. More porous investment in the mold, B. Narrow sprue diameter, C. Hollow sprue pin, D. Large reservoir
B: Narrow sprue diameter
Answer: B: Narrow sprue diameter 
Explanation: None