Natural unemployment: Unemployment is caused by some insurmountable reasons in the economy. It is unavoidable in any economy, and it is also normal unemployment. Based on the above definitions, which of the following do not belong to natural unemployment? ['Wang resigned because he thought his salary was too low during a year of working in a company.', 'An earthquake occurred in a certain place, the plant and equipment were destroyed, and the factory director relentlessly dismissed people who had worked for many years.', 'An enterprise is undergoing a restructuring, and some women with a low level of education have been laid off.', "Zhang violated the company's black box operation and was fired by the company after being found."]