State whether the following situations describe a between-subjects design or a within-subjects design.
(a) A biopsychologist tests the time course for the release of a neurohormone before, during, and following a task thought to cause its release.
(b) A sport psychologist compares mental functioning in a sample of athletes in four different sports.
(c) A college professor compares the average class grade for students in each of three sections of a statistics course.
(d) A behavioral psychologist allows a sample of children to play with four toys of various colors and has them rate how much they like playing with each toy. The psychologist compares mean ratings for each toy.