The correct answer is D) They believed political parties threatened the unity of a republic.
The authors of the Constitution want to avoid political parties because they believed political parties threatened the unity of a republic.
Since the very beginning, founding fathers such as General George Washington did not support the idea of having political parties because they considered that political parties could divide the American citizens into different factions. This represented the possibility that the political parties threatened the unity of a republic. People tended to overreact when emotions and feelings are present and political parties had the risk to play with the emotions of the citizens.