5)About two weeks into the study, a new TV program started airing in town. The program targeted kindergartners, using entertaining puppets to teach kids concepts like reading, science, math, history, and physical education. The show appealed mostly to girls, though, even using the title "Girls Get It Done" as a program tagline. The researchers found that there was no difference between female students in the math-based reading program and female students in the control reading program on the PICO post-test, though male students seemed to do much better in the math-based reading program than male students in the control reading program. Which internal validity threat is most likely occurring in this scenario?

a.Maturation

b.Regression to the mean

c.Selection

d.Mortality

e.Instrumentation

f.Testing

g.History

h.Interactions

i.Diffusion

j.No Threat