An example of a correct answer would be if the child and the doll were situated on the complete opposite sides of the mountain model with a tree on the child's side and a large mountain in the middle acting as a visual barrier. A preoperational child would claim that the doll could see the tree, whereas the concrete operational child would select a photograph without the tree since the mountain is large enough to block the tree from the doll's view. A concrete operational child would pass the Three Mountain Problem task.
