I think it's just a combination of numbers, and then it's a matter of sorting. The number required is only the serial number. I drew a picture. In fact, only five pictures are given here, but there should be six, which are two combinations of circles and boxes, two combinations of circles and triangles, and two combinations of boxes and triangles, and then I will sort them.

If you look at this picture, you should know what the numbers are at the bottom of that picture. Why are they arranged like this? Maybe it is easier for primary school students to sort out these figures.