In the Analytical Framework Describing How Republicans Managed to Break

In the analytical framework describing how Republicans managed to break the gridlock in Washington after they took power in 2001, which one of these statements falls under the structural level?

A) The sense of patriotism and shared threat arising from the 9/11 attacks created a brief period of Democratic-Republican and presidential-congressional cooperation in late 2001/early 2002.
B) Neither party enjoyed a commanding lead in party identification nationally during the 1990s or 2000s.
C) Major bills are passed by Congress and signed into law by President Bush.
D) The elections of 2000, 2002, and 2004 resulted in unified government, with Republicans in control of Congress (with the exception of 2002, when Democrats temporarily regained the majority in the Senate after one Republican senator defected) and the presidency.
E) Partisan warfare and scandals became standard fare in the mass media, making cooperation and civility in public affairs, in general, and between the parties, in particular, less likely.