The effect of the time of day a psychology class is taught on test scores is being studied in an experiment. Student ability has been identified as an extraneous factor that could also affect test scores. How can student ability best be addressed to minimize its effect in the experiment? A. Replication of the experiment at different times of the year B. Direct control of what textbook is used C. Randomization of students in morning and afternoon classes D. Blocking into groups based on the teacher of the class