Final answer:
The best measure of a school's selectivity is the rigor of its curriculum, which includes advanced placement classes, honors courses, and specialized programs.
Step-by-step explanation:
The best measure of a school's degree of selectivity is the rigor of curriculum. This refers to the level of difficulty and academic challenge present in the courses offered by the school. A highly selective school will have a rigorous curriculum that includes advanced placement (AP) classes, honors courses, and specialized programs.
While the other factors mentioned, such as the percentage of applicants accepted, the cost of tuition, and the graduation rate, may provide some insight into selectivity, they do not necessarily reflect the academic standards and rigor of the school.