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
Following is/ are the causes of 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 chronic cough and a normal or noncontributory chest radiograph belong to one of the following causes:i) Use of an angiotensin-conveing enzyme inhibitorii) Post-nasal drainageiii) Gastroesophageal reflux andiv) Asthma.