Four-year-old Morris is having lunch with his mother and sister. His mother pours milk into the shorter, wider glass in front of Morris and an equal amount of milk into a thinner, taller glass in front of his sister. Morris complains that his sister got more milk than he did. Even when his mother tries to explain that they both got the same amount, Morris insists he is right. In this example, Morris is demonstrating a lack of understanding of __________?
1) egocentrism
2) conservation
3) post-abstract thought
4) concrete operational thought
