A case study would be the most appropriate method to investigate which of these topics?

a. the ways in which the games of boys differ from the games of girls
b. the development of a male baby raised as a female after a surgical error destroyed his penis
c. the math skills of students in Japan as compared to those of U.S. students
d. physiological changes that occur when people watch violent movies
e. the relationship between childhood nutrition and physical development

b. the development of a male baby raised as a female after a surgical error destroyed his penis.