Concept:Unemployment caused by a mismatch between a worker's skills and the skills demanded by available jobs.Explanation:When a worker's skill becomes outdated due to changes in technology or production methods, they cannot easily find a job. This type of unemployment is called structural unemployment. It arises from changes in the structure of the economy, not from the business cycle or seasons. It is different from cyclical, seasonal, or frictional unemployment.Answer:A. Structural unemployment