The lower esophageal sphincter is responsible for _____.
a. allowing chyme to enter the stomach
b. preventing gastric contents from refluxing into the esophagus
c. adding digestive juices to the bolus of food as it descends the esophagus
d. allowing intermittent amounts of stomach contents to enter the duodenum
e. controlling movement of bile from the gallbladder to the small intestine