Who are the three dominant figures of the American Age of Realism and what are the differences in their understanding of the “truth”?

Who are the three dominant figures of the American Age of Realism and what are the differences in their understanding of the “truth”?

A.William Dean Howells, Mark Twain. Henry James.
B.Mark Twain and Howells seemed to have paid more attention to the "life"of the Americans.Howells focused his discussion on the rising middle class and the way they lived: Mark Twain preferred to have his own region and people at the forefront of his stories Henry James had apparently laid a greater emphasis on the"inner world"of man.