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
Which of the following is not an obstructive cause of mouth breathing: 
Select and explain. 
A. Deviated nasal septum., B. Short lip., C. Narrow maxilla., D. Obstructive adenoids.
B: Short lip.
Answer: B: Short lip. 
Explanation: Short lip is an anatomic cause.