What Is the Most Fundamental Difference Between Socialist Thought,and Modern

What is the most fundamental difference between socialist thought,and modern social-democratic parties?

A) Socialist thought promotes equality of result, whereas social democratic parties focus on equality of opportunity.
B) Socialist thought relies on revolutionary reform whereas social democratic parties respect constitutionalism.
C) Socialist thought calls for an end to the market economy, whereas social democratic parties try to use the market to achieve their objectives.
D) Socialist thought calls for deregulation, while socialist parties seek nationalization of resources.