According to Economists,one Reason Few Professional Athletes Have PhD's Is

According to economists,one reason few professional athletes have PhD's is that the

A) opportunity cost of going to graduate school is too high.
B) marginal benefit of going to graduate school is too high.
C) marginal cost of going to graduate school is too high.
D) comparative cost of going to graduate school is too high.
E) explicit cost of going to graduate school would be too high.