Schools normally schedule one subject, for example, Japanese, the first period, when you just do Japanese; then, say, arithmetic the second period, when you just do arithmetic. But here it was quite different. At the beginning of the first period, the teacher made a list of all the problems and questions in the subjects to be studied that day. Then she would say, "Now, start with any of these you like." So whether you started on Japanese or arithmetic or something else didn't matter at all. Someone who liked composition might be writing something, while behind you someone who liked physics might be boiling something in a flask over an alcohol burner, so that a small explosion was liable to occur in any of the classrooms.