Suppose an educational psychologist is carrying out an experiment in which grade school children hear one of four stories: (1) a stereotypical (and sexist) story in which a boy is the active hero while a girl just passively watches him, (2) a reverse stereotype story in which a girl is active while a boy just watches, (3) a story in which both a boy and a girl are active, or (4) a story in which both a boy and a girl are passive. Of the children who hear a given story, 15 are boys and 15 girls. After hearing the story (whichever of the four kinds it is), each subject is given an opportunity to work at the mildly frustrating task of using long-handled spoons to rearrange a terrarium in a narrow necked jar. The psychologist observes how long the subject persists at the task. This experiment has which kind of design?

(a) A one-way design in which type of story is the treatment variable.

(b) A one-way design in which sex of subject is the treatment variable.

(c) A two-way design in which type of story and sex of subject are the treatment variables.

(d) A two-way design in which type of story and persistence at the task are the treatment variables. Explain.