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: Radiology
Investigation of choice in diffuse esophageal spasm is 
Select and explain. 
A. Manometry, B. Esophagoscopy, C. Barium examination showing tertiary contractions, D. CT thorax
A: Manometry
Answer: A: Manometry 
Explanation: Investigation of choice for motor disorders (including diffuse esophageal spasm) is esophageal manometry.