This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bleeding from the GUT and diseases of esophagus, Subject name: Medicine
Diffuse esophageal spasm is best diagnosed by? 
Select and explain. 
A. Endoscopy, B. Manometry, C. Barium swallow, D. CT
B: Manometry
Answer: B: Manometry 
Explanation: Manometry is used to diagnose motility disorders (achalasia, diffuse esophageal spasm) and to assess peristaltic integrity prior to the surgery for reflux disease Esophageal manometry, or motility testing, entails positioning a pressure sensing catheter within the esophagus and then observing the contractility following test swallows. The upper and lower esophageal sphincters appear as zones of high pressure that relax on swallowing while the intersphincteric esophagus exhibits peristaltic contractions.