The correct answer is:
C. Active competition in the marketplace.
Explanation:
A market economy is an economic system in which supply and demand regulate the economy and individuals and private business own the resources, decisions in this economic system are made by individuals and private business without or with little government intervention.
Active competition in the marketplace is one of the most important factors because each producer gets to decide what and how much to produce, as well as the price, so competition leads to efficiency because it puts pressure on the producers to produce the best product at the best price, according to the demand and supply system, so that they can offer the best product in the market.