Final answer:
According to Marx, the fundamental source of stratification & inequality in capitalist societies is the exploitation of the working class by the capitalist class.
Step-by-step explanation:
According to Karl Marx, the fundamental source of stratification and inequality in capitalist societies is the division of people into two main groups: the bourgeoisie, who own factories and land, and the proletariat, who work in these factories. The bourgeoisie exploit the proletariat by paying them less than the value of their labor, resulting in the accumulation of wealth and power for the bourgeoisie while the proletariat struggle to make ends meet. Marx believed that this class conflict is the root cause of stratification and inequality in capitalist societies.