Which of the following, if true, would most seriously weaken the conclusion drawn above? A. While music is common in elementary school curricula, it is rarely taught in high school. B. On international tests of complex math skills, high-school students in this country performed no worse than did their counterparts from countries where problem solving is emphasized in higher grades. C. When presented with a math problem to solve, students in higher grades are more likely to arrive at different answers than students in lower grades. D. Older students tend to receive higher grades in math than younger students do. E. Universities in this country report a steady increase in the percentage of first-year students who qualify to take courses such as engineering that require advanced math.