Which statement is true?a. The process of differential reinforcement produces response differentiation. b. Melania has been working with a boy to shape his handwriting. At first, he could hold his pencil and write the letters of his name, but the marks were so faint that onecould hardly see them. Over time, Melania taught him to press his pencil hard enough so that people could easily see the mark he had made. The shaping procedure Melania used is an example of shaping across a response topography. c. It is not common for problem behaviors to be learned via shaping processes. d. In fading, behavior is changed by changing consequence stimuli, while in shaping, behavior is changed by gradually changing the antecedent stimuli.