The right answer is B. pancreas.
Diabetes is a chronic disease that can not be cured, but can be treated and controlled. It is due to the lack (or lack of use) of insulin (a peptid hormone).
Insulin is produced by the pancreas. It allows glucose (sugar) to enter the cells of the body for use as a source of energy. In a non-diabetic person, insulin performs well and cells have the energy they need to function.