Central School District Is Interested in Improving the Math Scores

Central School District is interested in improving the math scores of the enrolled fourth graders. They have elicited the assistance of Professor Glen. He informs the twenty fourth grade teachers that reviewing basic math facts is crucial to increasing the math scores. They are unconvinced. So, Professor Glen devised an experiment. All of the fourth graders were given the same math test. Then the teachers were randomly assigned to one of four groups. The groups differed on how many minutes per day were spent on reviewing basic math facts. All reviewing was identical and was conducted by completing and self grading of work sheets. The groups were ten minutes, fifteen minutes, twenty minutes, and thirty minutes. This continued for three months. At the end of the three-month period, the students were tested again on the same math test. In this experiment, the time spent reviewing is the

A) control.
B) dependent variable.
C) independent variable.
D) extraneous variable.