challenge: According to the book 'Race Against the Machine', what is the main reason for the lag in unemployment rates after the Great Recession of 2007-2008?
  
  A. Insufficient corporate profits to support hiring
  B. Lack of government investment in job creation programs
  C. Inefficient use of equipment and software by businesses
  D. Technological advancements that eliminate the need for many forms of human labor
  Answer: 