This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardio thoracic surgery  , Subject name: Anatomy
[{'content': 'Investigation to diagnosis of laryngopharyngeal reflux \nSelect and explain. \nA. Esophageal pH monitoring, B. Dual probe impedance pH monitoring, C. Barium esophagram, D. Scintigraphy', 'role': 'user'}, {'content': 'Answer: B \nExplanation: pH monitoring at the level of pharynx is not helpful because the acid refluxed is neutralised by the pharyngeal secretions Hence a dual (bifurcated) catheter measuring both pH and impedance is used across upper oesophageal sphincter thereby permitting detection of pharyngeal reflux Ref: Shackelford 8th edition Pgno: 222', 'role': 'assistant'}]