What is a likely major cause of high structural unemployment in the US?

High structural unemployment often arises when there is a significant mismatch between the skills that workers possess and the skills that employers need. In this context, option C correctly identifies that a major cause of high structural unemployment in the US can be attributed to changes in the job market where unemployed workers lack necessary training. As industries evolve, certain jobs may become obsolete while new jobs emerge that require different skill sets. If the workforce is unable to acquire these new skills through retraining or education, individuals may remain unemployed for extended periods, leading to structural unemployment.

This issue can stem from technological advancements, economic shifts, or other factors that change the nature of work, creating a gap between available job opportunities and the qualifications of job seekers. In contrast, other options may address different aspects of employment but do not directly correlate with the fundamental concept of structural unemployment in the same way. For instance, while immigration laws and turnover rates can impact employment dynamics, they do not inherently cause a mismatch of skills in the labor force. Similarly, increased demand for manual labor may lead to employment opportunities for some but does not address the underlying skill gap contributing to structural unemployment.