A is correct, because there's utopian socialism, scientific socialism, etc.
B is correct, because "utopian" describes a perfect world, which is a very idealistic thought.
C is correct, because capitalism is essentially the opposite of it, so the two are compared a lot, especially in terms of which one is better.
D is incorrect, because as socialism spread, economies changed all over the world. People in Europe began to have debates over whether socialism or capitalism was more beneficial.