What Problem Has Arisen, According to the Prospective Voting Model

What problem has arisen, according to the prospective voting model, as the Republican and Democratic parties have become more internally coherent in terms of policy preferences and ideologies?

A) Political conflict has become more intense because the stakes for each party in the outcome of any election become much more important than in a less partisan environment.
B) Political participation has become less important as each party's message is more obviously different from the other's.
C) The clarity of the Republican and Democrat positions has created a situation where they are not able to work out compromises.
D) Even as they move more toward the goals of the responsible party model, the Republicans and the Democrats are still unable to pass any meaningful legislature.
E) As the Republicans and Democrats have clarified their positions, the responsible party model has been proven the correct one, with little or no accompanying problems.