Which of the Following Is an Advantage of Communism

Which of the following is an advantage of communism?

A) Because all firms are owned by the same entity, research and development can be shared by all producers.
B) There is a much greater emphasis on advertising in communism than in other economic systems.
C) Prices send producers and consumers important signals about the value of resources and output.
D) Shared income increases the incentive to produce.