In a $0-1$ integer programming model, what does a decision variable value of $1$ typically represent?

A$.$ A constraint is satisfied

B$.$ A resource is fully utilized

C$.$ A particular option or decision is selected

D$.$ The optimal solution is achieved

In a transshipment model, what is the key difference compared to a standard transportation model?

A$.$ Transshipment models allow items to bypass supply and demand constraints by introducing surplus variables.

B$.$ Transshipment models ensure balanced transportation by adjusting costs at intermediate points. C$.$ Transshipment models simplify the network by eliminating the need for direct source$-$to$-$destination routes.

D$.$ Transshipment models include intermediate nodes that can serve as either additional sources or destinations in the network.