This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorders of Gastrointestinal System Including Diarrhea, Subject name: Pediatrics
The Gold standard investigation for Gastro-Oesophageal reflux disease is: 
Select and explain. 
A. Endoscopy, B. 24 hour esophageal pH recording, C. Oesophageal manometry, D. Measurement of length of lower oesophageal sphincter
B: 24 hour esophageal pH recording
Answer: B: 24 hour esophageal pH recording 
Explanation: 24 hour Esophageal pH recording provides a quantitative & sensitive documentation of acidic reflux episodes.