<span>He believed that they had a moral responsibility to use that wealth to lift up the conditions of everyone else in society. He felt that it was the duty of those of great means to be philanthropic to the point at which they did not have anything of their own at the end of their lifetimes.</span>
C is the answer you are looking for. A common idea isn't a moral, the generalization is the Main Idea, but not quite the moral. The thought of the characters almost never have the moral in them. Therefore, C is your answer.
