Which Property of Triton,the Largest Moon of Neptune,makes It Significantly

Multiple Choice

Which property of Triton,the largest moon of Neptune,makes it significantly different from all other major moons in the solar system?

A) an atmosphere of nitrogen and oxygen and water clouds
B) an orbit at right angles to the equator of the mother planet
C) an extremely dark, smooth surface, which prevented it from being discovered until very recently
D) an orbit direction opposite to the rotation and revolution of the mother planet