1. teacher flow: due to personal reasons, career development and other factors, the teaching staff of the school will change. In order to maintain the normal teaching order and quality, the school needs to recruit new teachers every year to fill the vacancy.

2. Enrollment expansion: With the adjustment of social needs and education policies, the school will expand the enrollment scale. In order to meet the teaching needs after the enrollment expansion, the school needs to increase the number of teachers to ensure that every student can get full education and attention.

3. Retirement of teachers: Over time, some teachers in the school will retire. In order to ensure the normal teaching work, schools need to recruit new teachers to fill the vacancies of retired teachers.