Which Is Probably True About the U

Which is probably true about the U.S. educational system?

A) Graduation rates are so low, that large external benefits could be realized by increasing the rate.
B) Graduation rates are high enough that external benefits associated with increasing the rate even further are probably very small or non-existent.
C) External benefits are a strong argument for free secondary education in the U.S.
D) None of the above.