Seventh grade, mainly to lay the foundation. You can choose books that explain synchronous exercises synchronously. Synchronous explanation includes instructions, complete solutions for teaching materials, colorful classrooms, top-class classrooms, full-featured lecture halls, teaching materials help and so on. Teaching is biased towards the explanation of problems, and less knowledge is explained; Textbooks are good at understanding all knowledge points, but there are relatively few topics and many words, which are boring; Colorful classes and champion classes have similar problems. If the lecture hall is full, the price will be high. There are many cartoons in the textbook Help. Color matching is good, not boring, and the overall solution is complete, the questions are complete, the methods are complete, the price is not expensive, and the cost performance is high. I recommend textbook help. If you practice synchronously, it is recommended to take a matching one.