This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ear, Subject name: ENT
All of the following from the boundary of MacEwen's triangle except 
Select and explain. 
A. Temporal line, B. Posterosuperior segment of bony external auditory canal, C. Promontory, D. Tangent drawn to the external auditory meatus
C: Promontory
Answer: C: Promontory 
Explanation: Bounded by Temporal line, the Posterosuperior segment of a bony external auditory canal, Tangent drawn to the external auditory meatus. Impoant landmark to locate mastoid antrum in mastoid surgery. Ref: Dhingra 6th edition