Practicing every day is a common exercise problem in the north. It is a difficult teaching aid in terms of difficulty, and it is a good choice for preview. What I know is the People's Education Edition, the Soviet Education Edition, and other versions are not very clear. You can find it yourself.

The experimental class is more difficult than practicing once every 53 days, and easier than learning to bully. Relatively speaking, it is quite good as a usual exercise. Our school chose the experimental class as the school's math exercise book.