when blood glucose concentration falls, what pancreatic hormone is secreted to stimulate release of stored glucose? insulin cholecystokinin glucagon secretin epinephrine

The right answer is glucagon.
Glucagon is a hormone secreted by the pancreas, whose role is to stimulate the breakdown of glycogen into glucose. It has an opposite action to the insulin.

Epinephrine rises also the blood glucose concentration. but it is secreted by the adrenal glands (and not the pancreas) in "dangerous" situations, and it acts by stimulating gluconeogenesis (synthesizing glucose from resources other than carbohydrated).

The correct answer is b