Answer: A is correct.
Explanation: this attitude makes him a humanist. He did not commit any crime (I believe), but he (as many others before him) did not evaluate sufficiently human nature. He believed that humans are better that they are and that is why he believed that they would be able to make "perfect society". Marx died in the 1880s and did not witness times when Communism entered into existence not as a theory, philosophy, doctrine but as regime. He did not witness the way how people put it into existence ...he was a pure theorist.