People Who Are Very ____________ May Seek Out So Much

People who are very ____________ may seek out so much environmental stimulation that they get into trouble. People who are very ____________ may be so overstimulated by their environments that they feel chronically overwhelmed and uncomfortable. Which brain structure is responsible for consistent differences in under- or overstimulation in personality?

A) extroverted; introverted; descending reticular activating system
B) extroverted; introverted; ascending reticular activating system
C) introverted; extroverted; descending reticular activating system
D) introverted; extroverted; ascending reticular activating system