Question

While Sola was away I took occasion to examine more minutely the room in which I found myself captive. The mural painting depicted scenes of rare and wonderful beauty; mountains, rivers, lake, ocean, meadow, trees and flowers, winding roadways, sun-kissed gardens—scenes which might have portrayed earthly views but for the different colorings of the vegetation. The work had evidently been wrought by a master hand, so subtle the atmosphere, so perfect the technique; yet nowhere was there a representation of a living animal, either human or brute, by which I could guess at the likeness of these other and perhaps extinct denizens of Mars.

Based on the passage, the reader can conclude that A Princess of Mars is a fantasy because it

is told by a narrator.
features a prisoner.
analyzes a piece of art.
is set on another planet.

Answer 1

"is set on another planet."

The passage mentions "denizens of Mars" and describes vegetation with different coloring, indicating an otherworldly setting—what makes it fantasy. The other options (having a narrator, a prisoner, or an art analysis) do not by themselves make a work fantasy.