A large city is planning for the Olympic Games which will be coming in a few years. The transportation system is being evaluated to determine what expansion is needed to handle the large number of visitors to the games.

Which of the following models would most likely help the city planners determine the capacity of the current system?

a. The transportation model.

b. The maximal-flow model.

c. The shortest-route model.

d. The minimal-spanning tree model.