According to the national center for educational statistics, the national graduation rate for public secondary schools in 2007 was 25.7% 50.4% 74.7% 100%

The National Center for Education Statistics is the part of the United States Department of Education's Institute of Education Sciences that collects, analyzes, and publishes statistics on education
According to the National Center for Educational Statistics, the national graduation rate for public secondary schools in 2007 was 50.4%.
In 2007, public school enrollment in the United States is expected to approach about 50 million students: 34.6 million in prekindergarten through 8th grade and 15.0 million in grades 9 through 12. 

Ithink the answer is b