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
Occlusal isthmus of a M.O. dental amalgam is resistant to fracture if: 
Select and explain. 
A. Pulpal floor depth is 1mm, B. Dove tail is present, C. Axiopulpal line angle is rounded, D. Unsupported enamel at the gingival cavosurface margin is planed
C: Axiopulpal line angle is rounded
Answer: C: Axiopulpal line angle is rounded 
Explanation: None