1. difficulty: classify the topics according to their difficulty, such as simple, medium and difficult.
2. Question type: classified according to the question type, such as addition, subtraction, multiplication and division, fraction, decimal, etc.
3. Grades: Students are classified according to grades, such as grade one, grade two and grade one of junior high school.
4. Theme: Classify the topics according to their themes, such as mathematics in life, interesting mathematics, competition mathematics, etc.