Final answer:
The incomplete maturation of the cerebral cortex in young teens is responsible for their inability to curb risky behavior or make long-term plans.
Step-by-step explanation:
The incomplete maturation of the cerebral cortex in young teens is responsible for their inability to curb risky behavior or make long-term plans. The cerebral cortex is the outer layer of the brain that is involved in executive functions such as decision making, impulse control, and planning ahead. It continues to develop throughout adolescence, which is why teenagers may engage in more risk-taking behaviors and struggle with making mature decisions.