Which of These Is NOT a Reason for the Rise

Which of these is NOT a reason for the rise of partisanship in Congress?

A) The Democrats having taken over the former states of the Confederacy, which has created a conflict within the Republican party.
B) The changing regional bases of the parties have created new alliances.
C) Partisan conflict and division is happening across the board in the country.
D) Party advocacy groups are pressured strongly to act as partisans as they go about their legislative tasks.
E) In the electorate and among the members of Congress, Democrats are becoming more liberal and Republicans are becoming more consistently conservative.