There are 20 classes in a grade * * *, and the student number of each class is 1 ~ 50. In order to exchange learning experience, students with learning number 22 in each class are required to stay in school.
There are 20 classes in one grade, and the student number of each class is 1 ~ 50.
Students in each class with 22 students are required to participate in exchange activities.
The sampling method used here is systematic sampling,
So choose D.