DrPerkins Places Rats That Always Lived in a Deprived Environment

Multiple Choice

Dr.Perkins places rats that always lived in a deprived environment into a new "enriched" environment with an exercise wheel and toys to stimulate the rats' problem-solving capabilities.After two weeks in the enriched environment,the rats seem more alert than they were before.Dr.Perkins decides to try the same thing with a new sample of rats,which also seem more alert after spending two weeks in the new environment.This means that Dr.Perkins replicated his findings on the second sample of rats.However,when Dr.Perkins wants to know whether the rats became more alert because of the exercise wheel or because of the toys,he is concerned with the issue of _____________.

A) reliability
B) measuring gradients
C) internal validity
D) ecological validity