Xavier, 16, invites a group of his high school friends to swim in a neighbor's pool late at night while that neighbor is away. They climb the fence and jump in, playing wildly and loudly in the water. Just a few minutes later, the police arrive. How does adolescent brain development help explain Xavier's poor decision making?

His prefrontal cortex is underdeveloped.    

Explanation:

The "prefrontal cortex" is also written as "PFC" and is defined as the "cerebral cortex" that covers the front part of a person's frontal lobe of the brain. The prefrontal cortex is being implemented or is significant in planning or developing personality expression, moderating social behavior, complex cognitive behavior, and decision-making process, etc.

A person's prefrontal cortex is being fully-developed or matured at the age of twenty-five years and therefore an adolescent has underdeveloped prefrontal cortex.

As per the question, Xavier's poor decision making is due to the fact that his prefrontal cortex is underdeveloped.

first, the romans stayed isolated because they had to defend their own territories from neighboring cities that were harassing them, like the etruscans. second, once the romans managed to defeat their neighbors, and started to expand their territory, they started to build roads and bridges. finally, now that the romans have covered their territory with roads functioning as highways, they could mobilize their legions faster to assemble larger military units in a specific place