A) friendship is an important survival tool.
Answer:
Changes in the Prefrontal Cortex
As the prefrontal cortex matures, teenagers can reason better, develop more control over impulses and make judgments better. In fact, this part of the brain has been dubbed "the area of sober second thought." The fact that this area was still growing surprised the scientists.
Explanation:
D, as extrinsic means external stimulus. Andrew may not necessarily enjoy doing extra math problems, but there is an incentive, which is good grades. With the other 3 people, there is no incentive other than enjoyment.
