D Question 4 10 pts A minimum cost flow problem involves which of the following? O an objective to maximize the number of routes O negativity constraints constraints to require shipment on every possible route strictly less than constraints to limit shipments nodes where the net amount of flow generated is a fixed positive number Question 5 10 pts What property is necessary for a minimum-cost flow problem with only fixed-requirement-supply constraints and fixed-requirement-demand constraints to have solutions? O non-positivity constraints O demands sum to zero supplies sum to zero the sum of the supplies from the supply nodes equals the sum of the demands at the demand nodes O the sum of the supplies from the supply nodes is less than the sum of the demands at the demand nodes