Final answer:
The description from The Red Badge of Courage best supports the central idea of b) The definition of courage.
Step-by-step explanation:
The passage from 'The Red Badge of Courage' highlighting the protagonist's internal struggle and anticipation of danger as he faces the fears associated with war.
As the protagonist contemplates the 'mystic gloom' and the 'red eyes across the river' growing larger, resembling 'orbs of a row of dragons,' he embodies the sense of facing unknown dangers and the psychological battle within, which is at the core of defining courage.
The passage conveys the inner turmoil and the looming presence of fear and challenge that the protagonists must confront, showcasing the central theme of grappling with personal courage in the face of war.
Therefore the best central idea of the passage would be b) The definition of courage.