This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'To diagnose GERD , in 24 hour ambulatory pH testing the percentage of the day that the pH was less than 4 is: \nSelect and explain. \nA. > 20%, B. > 1%, C. > 5 %, D. > 1 %', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The percentage of the day that the pH was less than 4 with values exceeding 5% indicative of GERD.Intraluminal impedance monitoring can be added to pH monitoring to detect reflux events irrespective of whether or not they are acidic. Ref : Harrison, E-18, P- 2428', 'role': 'assistant'}]