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: Medicine
[{'content': 'GERD is best diagnosed by? \nSelect and explain. \nA. 24 hour pH Monitoring, B. Upper GI endoscopy, C. Barium meal follow through, D. Barium Swallow', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) 24 hour pH monitoringRef.: Harrison 19th ed. / 261-2* Ambulatory 24-hour pH monitoring is the criterion standard in establishing a diagnosis of GERD, with a sensitivity of 96% and a specificity of 95%. It quantifies the gastroesophageal reflux and allows a correlation between the symptoms of reflux and the episodes of reflux.* However the diagnosis can be established on basis of Upper Gastrointestinal endoscopy with esophageal manometry.', 'role': 'assistant'}]