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
Eustachian tube patency is seen by- 
Select and explain. 
A. Valsalva, B. Methylene blue test, C. Tonybee test, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: None