The correct option is A Insulin
Islets of Langerhans are the functional units of the endocrine part of the pancreas. There are five types of cells in an islet: alpha cells that make glucagon, which raises the level of glucose (sugar) in the blood; beta cells that make insulin; delta cells that make somatostatin which inhibits the release of other hormones in the body and PP cells. Thus, the correct answer is option A.