This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Medicine
The gold standard for diagnosis of gastroesophageal reflux disease (GERD) is 
Select and explain. 
A. Endoscopy, B. Barium swallow, C. Esophageal manometry, D. 24-hours ambulatory pH monitoring
D: 24-hours ambulatory pH monitoring
Answer: D: 24-hours ambulatory pH monitoring 
Explanation: The most sensitive test for diagnosis of GERD is 24-h ambulatory pH monitoringRef: Harrison; 19th edition; Page no: 1894