There are two schools, which had national standardized tests. The average test score was 80 for classroom A and 70 for classroom B after the No Child Left Behind policy was adopted. After inspecting the answer sheets, the Board of Education suspected of cheating in classroom A, and ordered both classes to retake the same test again (and strictly monitor to prevent cheating during the retake). In the retaken test, the average score was 70 for classroom A and 80 for classroom B. The net impact of cheating: Preventing cheating decreases class average score by c) points. 20 points O points 10 points 30 points