Identify the factors that were responsible for the shrinking size of the american middle class after the early 1970s.
a) the emergence of the low-wage service sector
b) greater demand for higher-skill jobs
c) a more regressive federal income tax
d) an expanding income gap between the highest paid executives and employees in the middle ranks

Explanation:

There were many factors that contributed to the shrinking of the american middle class in the 1970s, first of all the the emergence of the low-wage service sector  (mainly blue collar job positions) and on the other hand a  greater demand for higher-skill jobs for top companies which led to an expanding income gap between the highest paid executives and employees in the middle ranks

c) troops march forward in close formation against newer, more accurate weapons