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
At birth, child shows marked convex profile. This is due to: 
Select and explain. 
A. Protruded maxilla, B. Retruded mandible, C. Large sized maxilla, D. Small sized mandible
D: Small sized mandible
Answer: D: Small sized mandible 
Explanation: None