Concept:The Islets of Langerhans are clusters of hormone-producing cells located within the pancreas.Explanation:These clusters were discovered by Dr. Paul Langerhans. They contain three main cell types: alpha cells (release glucagon), beta cells (release insulin), and delta cells (release somatostatin). These hormones regulate blood glucose levels. The pancreas is the only organ that houses these islets. The other options – stomach, liver, and heart – are associated with digestion, detoxification, and blood circulation, respectively, and do not contain islets.Answer:The correct answer is option C. Pancreas.