The answer would be A. When supply exceeds demand
This is because there is plenty supply for the forest without animals dying from things such as, lack of food.
When demand exceeds supply it throws an ecosystem off because some animals aren't getting the food they need and therefor dying. So that eliminates answers C. and D.
When supply and demand are both 0 that means that there are no animals to demand and there are no supplies for demand leaving no sustainable ecosystem.
