The correct answer is D) the existence of social classes.
Socialism is similar to capitalism in the existence of social classes.
Capitalist economies are based on private property and the free market. In Capitalism, the government does messes up with the economy, which means that it does not exert strong regulation. The free market regulates the economy through supply and demand. People can have private property and increase their wealth. In Socialist countries are the opposite, there is strong central government control in the economy and most of the industry is owned by the government that dictates what to produce, when, how, and the prices of products. In both systems, there are social classes.