Fundamental differences between social class, slavery, caste and property ownership systems are:

• Social class inequalities depend on economic reasons like job, poverty, prosperity and income. Inequality thrived with the belief system of religion, law, pressure and oppression. 

• Social classes are not clearly and obviously distinct from each other. Distinctions between classes are uncertain and vague. For example, it is difficult to say where the working class ends and middle class begins.

• Social classes are not supported by legal inequalities. Everybody has equal rights before the law. Upper classes do not have legal authority on the lower classes. 

• Religious and legal restrictions or limitations are not imposed for marriages between people from different social classes. Actually, most people get married to people from similar class positions; besides, in theory, they can get married to whoever they wish.

• Modern societies are open systems. There are no religious or legal restrictions for individuals or groups that may affect moving from a class to another. Social mobility between classes is possible. Individuals’ positions in social classes do not depend on inborn and ascribed (obtained) conditions. Qualities like knowledge or skill, which are earned by education, affect social class positions. At the same time, a child’s familial social position affects her/ his life and position of class in the modern society as well.

Therefore, the correct option is E.