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': 'IOC for G.E.R.D: \nSelect and explain. \nA. 24 HR pH monitoring, B. Upper G.I. endoscopy, C. Ultrasound, D. X ray abdomen', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) 24 HR pH monitoringRef: Harrison 19th ed. 1261-62* 24 hour pH monitoring is done for GERD.* Components of 24 hour pH monitoring:# Percent total time pH < 4# Percent upright time pH < 4# Percent supine time pH < 4# Number of reflux episodes# No. of reflux episodes in 5 minutes# Longest reflux episode (minutes)Remember: This method is also used for detection of laryngo-esophageal reflux that causes asthma, laryngospasm.', 'role': 'assistant'}]