Which of the following is an example of response maintenance?
One month after having learned the skill of tying shoes, Billy is able to tie his shoes everyday as he gets ready for school.
After learning to say "hi" as a greeting, Sally has started to greet people by saying, "Hello," and "What's up?"
After learning that the small white dog down the street was named Rusty, Mary started calling her family's white cat Rusty.
Billy has learned to wash his hands at school, at home, and at his job.