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: ENT
Choanal atresia is due to persistence of ? 
Select and explain. 
A. Bucconasal membrane, B. Oropharyngeal membrane, C. Laryngo tracheal fold, D. Tracheoesophageal fold
A: Bucconasal membrane
Answer: A: Bucconasal membrane 
Explanation: Choanal atresia is an abnormality of canalization during development of the nasal passages. It involves bone and/or soft tissue and may result in either paial (choanal stenosis) or complete obstruction of the posterior nasal airway. The most widely accepted mechanism for the development of choanal atresia is the persistence of the bucconasal membrane beyond the sixth week of gestation, but abnormal migration of cephalic neural crest cells following neural tube closure also has been implicated. The incidence of choanal atresia is 1 in 7000 to 8000 live bihs. It is more common in females (2:1), more likely to be bony or cailaginous than membranous (9:1), and more commonly unilateral and right-sided (2:1).