I don't think it's necessary. These are for people who have no chance to study at school, or for people to browse. I think it is enough to read my own textbooks, which are the essence of thousands of choices. I can read books very well, plus the teacher's extracurricular questions in class, which is invincible. I don't like those! ! ! Besides, you don't have time to watch these. Finally, you put them under the table. You haven't seen them much! ! !