This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pharynx, Subject name: ENT
Unilateral middle ear serous effusion in an adult, most common cause is 
Select and explain. 
A. TB, B. Foreign body, C. Nasopharyngeal carcinoma, D. CSOM
C: Nasopharyngeal carcinoma
Answer: C: Nasopharyngeal carcinoma 
Explanation: "In adults presenting with a unilateral middle ear effusion, the possibility of a nasopharyngeal carcinoma should be considered""A high incidence of NPC (Nasopharyngeal carcinoma) in South East Asia and southern China correlates with the high incidence of OME (Otitis Media with Effusion) in adults in these regions"Ref: PL Dhingra, Diseases of Ear, Nose & Throat, 7th edition, pg no. 279 - 286