Concept:Structural unemployment is caused by a mismatch between a worker's skills and the skills demanded by available jobs.
Explanation:The civil engineer cannot find a paid engineering job because his specific skill is not currently in demand.
He then accepts a primary school teaching job, which does not match his professional training.
This situation is not due to a short job search or seasonal changes.
It arises from a long-term mismatch between his qualifications and the types of jobs available in the economy.
Therefore, it is a clear example of structural unemployment.
Answer:A. structural unemployment