The Percentage of Total Hours Worked by the Supply of College-Educated

The percentage of total hours worked by the supply of college-educated workers compared to the percentage of total hours worked by high-school educated workers has been:

A) constant.
B) climbing steadily to about 20 percent.
C) falling steadily to about 50 percent.
D) climbing steadily to about 50 percent.
E) doing none of the above.