A researcher found that college students between the ages of 20 and 23 performed better on a memory task in a low-noise condition than in a high-noise condition. Another researcher wants to repeat this study by adding age as a variable, using the 20-23 and 68-79 age groups. He predicts an interaction between the age and noise variables. In this scenario, the new researcher is questioning the________validity of the original study. a. statistical b. internal c. external d. interactional