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
Nasopharyngeal Ca causes deafness by: 
Select and explain. 
A. Temporal bone metastasis, B. Middle ear infiltration, C. Serous effusion, D. Radiation therapy
C: Serous effusion
Answer: C: Serous effusion 
Explanation: Nasopharyngeal carcinoma spreads to Eustachian tube, blocks it and causes Serous Otitis Media which in turn causes Conductive hearing loss.