Structural unemployment is primarily caused by:

Structural unemployment occurs when there's a mismatch between the skills that workers possess and the skills that employers need. This might be due to rapid technological advancements, shifts in consumer demand, or changes in the economy that make certain skills obsolete. As industries evolve, some workers may find themselves without the necessary skills for available jobs, thereby leading to long-term unemployment.

For example, if a manufacturing sector shifts to automation, workers who previously held jobs that required manual labor may lack the technical skills required for new roles in that industry. In this context, retraining or further education can be essential for these individuals to become employable again.

The other options describe circumstances related to labor dynamics but do not directly address the fundamental issue of skills mismatch that characterizes structural unemployment. Natural fluctuations in labor supply primarily deal with cyclical trends, seasonal changes refer to employment patterns related to certain times of the year, and changes in government policy can influence employment levels but do not inherently create a skills gap.