B, because the communists believed that there would be a revolution from the working people. They would stand up agains the higher classes and then there would be a situation in which the proletariat would have the power and eventually, the society would change in one without classess. And socialists didn't want to be so violent and tried to get similar results in a 'normal' way.
Answer: Utopian socialists believed that a classless society could be created peacefully, while communists believed that it could only occur through a violent revolution.
