Asked by researchers to sort objects by shape, most toddlers in a large study had no trouble doing so. When subsequently told to sort by color, the toddlers seemed to have difficulty following the new rule and almost invariably persisted with their first approach. The researchers suggest such failures to adapt to new rules often result from insufficient development of the prefrontal cortex in toddlers. The cortex is essential for functions like adapting to new rules, yet is slow to mature, continuing to develop right into adolescence. Which one of the following is most supported by the information above? ['Skill at adapting to new situations is roughly proportional to the level of development of the prefrontal cortex.', 'The maturing of the prefrontal cortex is more important than upbringing in causing the development of adaptive behavior.', 'Toddlers unable to sort objects by color tend to have a less developed prefrontal cortex than other children of the same age.', 'Certain kinds of behavior on the part of toddlers may not be willfully disobedient.']