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
True about cholesteatoma -a) Benign tumourb) Bone erosion presentc) MC cause of conductive deafnessd) Found in apex of petrous bone commonlye) Contains cholesterol 
Select and explain. 
A. c, B. bd, C. ab, D. ac
B: bd
Answer: B: bd 
Explanation: None