The Wage Rates of Southerners Have Been Slow to Converge

The wage rates of Southerners have been slow to converge to the higher wage rates of Northerners.Which of the following is a likely reason for this?

A) Tariffs by Northern states on goods made in the South remain high.
B) Displaced Northern workers have been not been able to find other well-paying jobs.
C) Southerners find it hard to understand the Northern accent.
D) It is costly to move production from the North to the South.