People Who Grew Up in the Western Part of Aquilonia

People who grew up in the western part of Aquilonia have an accent distinct from people who grew up in the eastern part of the country. People from the west also receive lower wages than people from the east. From this information alone, which of the following is not a possible explanation for this wage differential?

A) Discrimination against people from the west exists.
B) People from the east receive compensating differentials.
C) People from the west have lower levels of human capital.
D) People from the east put forth less effort in their work.