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: Pathology
Mouth opening is considered to be restricted when the distance is 
Select and explain. 
A. Less than 40 mm, B. Less than 50 mm, C. Less than 53 mm, D. Less than 58 mm
A: Less than 40 mm
Answer: A: Less than 40 mm 
Explanation: None