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
Simple mastoidectomy is done in -a) Acute mastoiditisb) Cholesteatomac) Coalescent mastoiditisd) Localized chronic otitis media 
Select and explain. 
A. a, B. bc, C. ac, D. b
C: ac
Answer: C: ac 
Explanation: Simple mastoidectomy is used in acute coalescent mastoiditis.