From 1982 to 2000, the Relative Wage of Nonproduction to Production

From 1982 to 2000, the relative wage of nonproduction to production workers in U.S. manufacturing and their share of total employment in U.S. manufacturing increased. One logical explanation would be:

A) that their wages fell in real terms.
B) that there was a decrease in demand for skilled workers.
C) that due to increased productivity or demand for products, there was a relative increase in demand for skilled workers.
D) that minimum wage increases shifted the demand for workers toward skilled workers.