This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Medicine
The investigation of choice to detect gastrinoma le<< than 5 mm size is- 
Select and explain. 
A. Endoscopic ultrasound, B. Octreotide scan, C. CT scan, D. Poal venous sampling
A: Endoscopic ultrasound
Answer: A: Endoscopic ultrasound 
Explanation: Investigations Upper gastrointestinal endoscopy is the investigation of choice and should be performed promptly in any dyspeptic patient with 'alarm features' . Multiple biopsies from the edge and base of a gastric ulcer are required. Barium meal is a poor alternative, since any abnormalities must be followed by endoscopy and biopsy. Ref Davidson edition23rd pg804