Incomes May Be Skewed in Favor of Some Groups Rather

Incomes may be skewed in favor of some groups rather than others because

A) in competitive markets, all workers receive equal pay for equal work.
B) some people will invest more in themselves to improve their productivity and income than others.
C) control over wages accrues more to those who work in competitive markets.
D) the members of these groups belong to a labor union, and this does not happen outside labor unions.