Ashley is taking a class on Piaget and as part of an assignment, has to interview children. She gives 7-year-old Andrew a bag of red and blue candies. They discuss how the candies are made of chocolate. Andrew counts the candies-7 red and 14 blue. Ashley asks, "Are there more blue candies or chocolate candies?" Andrew looks at her and laughs: "Of course there are more chocolate candies-they are all made of chocolate." This demonstrates that Andrew understands the concept of ___.