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: Surgery
A patient present with dysphagia of 4 weeks duration. Now he is able to swallow liquid food only. Which of the following is the one investigation to be done ? 
Select and explain. 
A. Barium studies are the best in this case, B. Upper GI endoscopy is to be done, C. CT scan is needed, D. Esophageal manometry
B: Upper GI endoscopy is to be done
Answer: B: Upper GI endoscopy is to be done 
Explanation: Answer is 'b' i.e. Upper GI endoscopy is to be done