Correspondence teaching is based on planned, organized and guided self-study, and centralized face-to-face teaching is organized. Face-to-face teaching time is usually winter and summer vacation. This form of study is also suitable for candidates who study on the job and have less spare time. The form of off-the-job study is generally full-time face-to-face, similar to ordinary higher education. Candidates mainly attend classes in adult education institutions, and teachers teach face to face. Class time is usually Monday to Friday.