Why are communism and capitalism diametrically opposed?

A. One of the goals of communism is free trade among all its citizens, whereas governments in capitalist economies prevent free trade.
B. Communism relies on bartering, whereas capitalism relies on the exchange of money for goods, and services in the free market.
C. One of the goals of communism is to eliminate social classes, whereas capitalism leads to significant differences in social classes as well as wealth inequality.
D. Under communism, goods are produced based on want, whereas goods are produced based on need under capitalism.

C. One of the goals of communism is to eliminate social classes, whereas capitalism leads to significant differences in social classes as well as wealth inequality.