Returning to education is a theory that believes that a person's life should be a continuous and alternating process of learning and work, a process that is mutually combined, and adults who receive compulsory education or basic education or even after higher education should return to school to study when needed. According to the above definitions, Which of the following belong to return education (). ['Nine-year compulsory education.', 'A technician from a factory recharges English at the staff night school held by the unit.', 'Kindergarten preschool education.', 'Secondary vocational school students participate in a one-year internship after two years of full-time study.']