Sean loves the movie cars but he has low communication skills and cannot make a request to watch the movie. sean’s rbt begins to model saying the word 'cars' and then immediately turns on the movie. eventually, sean makes the 'c' sound. sean’s rbt begins turning the movie on when he makes that approximation. later, sean adds the 'a' sound saying 'ca'. again, his technician stops reinforcing the previous approximation, and only reinforcing the 'ca'. finally, sean can say the entire word 'cars' when he wants to watch the movie. what process sean acquire this skill?