<prompt> 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 ?Barium studies are the best in this caseUpper GI endoscopy is to be doneCT scan is neededEsophageal manometry  <response>: Answer is b i.e. Upper GI endoscopy is to be done 