The rising income gap among highly educated workers in the United States:

A) is an important feature of the increase in income inequality.
B) has not been a cause of concern for income inequality policy makers.
C) is less of a concern than is the effect of increased immigration on income inequality.
D) has been present for the past 80 years.

The question explicitly states that the rising income gap among highly educated workers is a feature of the increase in income inequality, making option A the correct answer. Option B is incorrect as policymakers have indeed expressed concern over this issue. Option C is also incorrect as increased immigration is not specifically mentioned in the question and is not directly related to the income gap among highly educated workers. Option D is also incorrect as there is no information provided on the historical presence of this income gap.