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
Lower limit of retropharyngeal space is at ? 
Select and explain. 
A. C 7, B. Bifurcation of trachea, C. 4th esophageal constriction, D. None
B: Bifurcation of trachea
Answer: B: Bifurcation of trachea 
Explanation: Ans. is'b'i.e., Bifurcation of tracheaRetropharyngeal space is divided into two lateral spaces (space of gillette) by a fibrous band.Retropharyngeal space is limited above by the base of skull and below where the alar fascia fuses with buccopharyngeal fascia at the level of T4 and carina (bifurcation of trachea).