The face of the water, in time, became a wonderful book — a book that was a dead language to the uneducated passenger, but which told its mind to me without reserve, delivering its most cherished secrets as clearly as if it uttered them with a voice. And it was not a book to be read once and thrown aside, for it had a new story to tell every day.
—Life on the Mississippi,
Mark Twain

Which theme of the late 1800s does this passage embody?
A - the lack of equal rights
B - the triumph of reality over illusion
C - the appeal of the western frontier
D - sacrifice and endurance