One of the most common digestive problems involving the esophagus is

There are many digestive problems involving the esophagus (e.g. achalasia, squamous cell carcinoma of the esophagus, etc), but one of the most common esophageal diseases are heartburn or reflux disease also known as gastroesophageal reflux disease or GERD. GERD is characterized by the backflow of the stomach acids to the distal end of the esophagus causing damage and erosion. In chronic cases of GERD, the epithelium of the esophagus transforms from stratified squamous to columnar with goblet cells and this is called columnar metaplasia or Barrett's esophagus. This can predispose the patient to the risk of developing esophageal adenocarcinoma.

I’m going to go with b!