9)After seeing the pre-test PICO scores, the researchers were concerned about some of the kindergarteners who scored very low. To make sure these low scoring students would benefit from the study, the researchers made sure that these students were assigned to the math-based reading program while students who had moderate or high pre-test PICO scores were randomly assigned to either the math-based reading program or the control reading program. The researchers found that students in the math-based reading program and the control reading programs performed similarly on the PICO post-test at the end of the study. 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