This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oesophagus, Subject name: Surgery
Gold Standard investigation for GERD- 
Select and explain. 
A. 24 hour pH recording, B. Endoscopy, C. Ultrasound, D. Magnetic resonance imaging
A: 24 hour pH recording
Answer: A: 24 hour pH recording 
Explanation: Ans. is 'a' i.e., 24 hour pH recording Diagnostic measurement in GERD* 24- hour pH recording is the 'gold standard' for diagnosis of GERD* TILOSRs are the most important manometric findings in GERD* The length and pressure of the LOS are also important