Final answer:
In a longitudinal study, researchers observed an increase in the integration of emotion and cognition in the brain areas of college students, reflecting advancements in complex thinking abilities and the developmental trends of personality traits such as conscientiousness.
Step-by-step explanation:
In a longitudinal study of 18-year-old students at the beginning and end of their first year in college, researchers found increases in the brain areas that integrate emotion and cognition. This aligns with the knowledge that during adolescence and young adulthood, individuals develop more complex thinking abilities and advance in their ability to reason abstractly. Cognitive development includes improvements in existing skills such as processing speed and efficiency. Furthermore, the Big Five personality factors, which include conscientiousness, show that certain personality traits like conscientiousness tend to increase into middle age. These developments in the brain are critical for young adults as they navigate their way through college and begin to lay the foundation for their future careers and personal lives.
Therefore, the correct answer to the student's question would be: C) emotion; cognition.