Declining availability of unskilled workers was not an effect of increased migration to cities during the early 20th century
Explanation:
Contrary to the statement given, the coming of the various waves of people from other countries into USA provided a great and cheap source of unskilled labor which they were wont to do as they were desperate for work.
The Jewish, German and Irish and Italian settlers in the USA adopted the American identity but took their time in developing their capital during which they served as the working class of the country for time working jobs that are classified as unskilled labor.