2)The research study began one week into the semester. All kindergarten students were new to the school environment (they are kindergartners after all!), and they were unfamiliar with the classroom, the teacher, and taking tests in general. When the study ended a month later, the students were all much more familiar with how school worked. In terms of the research study, the researchers found that students in the math-based reading program did not differ in their PICO post-test scores compared to 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