This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pharmacology
The gold standard for diagnosis of gastroesophageal reflux disease (GERD) is not related-surgery 
Select and explain. 
A. Endoscopy, B. Barium swallow, C. Esophageal manometry, D. 24-hours pH monitoring
D: 24-hours pH monitoring
Answer: D: 24-hours pH monitoring 
Explanation: .