This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nose and paranasal sinuses, Subject name: ENT
Choana is: 
Select and explain. 
A. anterior nares, B. Posterior nares, C. Tonsils, D. Larynx
B: Posterior nares
Answer: B: Posterior nares 
Explanation: Posterior nares Nasal cavity: Nasal fossae are two irregular cavities extending from the mucocutaneous junction with the nasal vestibule in front(anterior nares) to the junction with the nasopharynx behind(posterior nares or choanae) Ref.Dhingra 5/e,p 150.6/e,p 135.