One or Two Generations Ago,fewer Canadians Completed Post- Secondary Training

One or two generations ago,fewer Canadians completed post- secondary training and education.One explanation for this is

A) a decrease in demand for more education in recent years.
B) that the opportunity cost of post- secondary education has increased.
C) wage differentials due to formal education have diminished over time.
D) a negative relationship between the acquisition of human capital and overall earnings.
E) the relative wage of more highly educated people has increased in recent years.