Answer:
D. Mixed economies are fast replacing market economies.
Explanation:
" A mixed economic system has features of both a command and a free market system. A mixed economy is partly controlled by the government and partly based on the forces of supply and demand.
Most of the main economies in the world are now mixed economies, which operate under a mix of socialism and capitalism."
Reference: Hall, Mary. “Command vs. Mixed Economy: What's the Difference?” Investopedia, Investopedia, 13 Sept. 2019