Which Statement Is TRUE Regarding the Islet Cells of the Pancreas

Which statement is TRUE regarding the islet cells of the pancreas?

A) $\alpha$ cells secrete glucagon to stimulate glycogenolysis in skeletal muscle.
B) $\alpha$ cells secrete glucagon to stimulate glycolysis liver.
C) $\beta$ cells secrete glucagon to stimulate glycogenolysis in liver.
D) $\beta$ cells secrete insulin to stimulate glucose uptake by skeletal muscle, the liver, and adipose tissue.
E) $\alpha$ cells secrete insulin to stimulate glycolysis in skeletal muscle.