This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Larynx, Subject name: ENT
Following is/are the causes of a chronic cough with noncontributory chest radiograph? 
Select and explain. 
A. Asthma, B. Post nasal drip, C. GERD, D. All the above
D: All the above
Answer: D: All the above 
Explanation: 90% of patients who have a chronic cough and a normal or noncontributory chest radiograph belong to one of the following causes:Use of an angiotensin-conveing enzyme inhibitor;Post -nasal drainage;Gastroesophageal reflux; andAsthmaRef: PL Dhingra, Diseases of Ear, Nose & Throat, 7th edition