The correct answer is A. Class conflict
Step-by-step explanation:
Karl Marx was an important economist, philosopher, and theorist from Germany. As part of this theories and proposals Karl Marx stated the human history and human societies had evolved mainly due to the class conflict that was the struggle between those who own the power and means of production and those who do not, for example, between the proletariat (workers) and those that owned the factories and means of production (bourgeoisie). Therefore, Karl Marx believed that history was the story of class conflict that emerges between different sectors of society and makes society change over time.