Correct answer: A. Because it moved toward ending feudal privileges
Explanation: The direct answer is option A: because it moved toward ending feudal privileges. The night of 4 August 1789 was important because the National Assembly adopted measures against the old feudal system. Before the Revolution, peasants and other ordinary people were burdened by feudal dues, obligations and privileges enjoyed by nobles. During the night of 4 August, representatives agreed to abolish or give up many feudal privileges. This attacked the legal and social inequalities of the old regime, so it was a social step of the Revolution. Option A is correct because removing feudal privileges changed the relationship between privileged groups and common people. Option B, electing a new king, is wrong because the event was not about choosing a monarch. Option C, building the Bastille, is wrong because the Bastille already existed and was stormed on 14 July. Option D, stopping the Estates-General, is wrong because the revolutionary representative process continued; the event concerned feudal privileges, not ending that meeting. The word “social” is important: the change affected social hierarchy and privileges, not merely a military event. Remember the date pair: 14 July challenged royal authority, while 4 August attacked feudal privileges. A common mistake is to describe 4 August as the storming of the Bastille.