The first question of classification: The key to this question is to teach children to fill in from 1 to 10 in turn. For example, if 1 is a terrestrial animal, then write 1 after the terrestrial animal, 2 after the terrestrial animal, 2 and 3 after the flying animal, that is, 3 after the flying animal, but if you can't find out what the terrestrial animal is, it will lose its statistical significance.

Terrestrial animals: 1 2 5 6

Flying animals: 3 8 10

Aquatic animals: 4 7 9