The statement that "there was no government intervention in the economy" best describes why capitalism can be considered a free market economy. In a free market economy, prices, production, and distribution of goods are determined by the forces of supply and demand without significant government intervention. This allows individuals and businesses to operate independently, make their own economic choices, and compete freely in the marketplace.
Other statements provided, such as the ability for people in lower classes to rise up or the creation of regulations by the government, do not align with the definition of a pure free market system, which emphasizes minimal or no government involvement. Social classes can exist in a free market economy, as economic disparities often arise from differing levels of capital and opportunity.