Your teacher seriously needs to rework the wording on these questions. The one on Pluto was poorly worded, and this one is even worse.
A. The retrograde rotation of Triton is not an exception. At least not for the gas giant planets (Jupiter, Saturn, Uranus and Neptune).
The gas giant planets have large numbers of small "irregular" moons in highly inclined or elliptical orbits, thought to be captured asteroids or Kuiper belt objects (or fragments thereof), and the majority of these exhibit retrograde motion: 48 retrograde to 7 direct for Jupiter, 29 to 9 for Saturn, and 8 to 1 for Uranus. Neptune is somewhat different: it seems to have captured its only surviving large moon, the retrograde but otherwise regular Triton, from the Kuiper Belt. The six irregular moons beyond Triton's orbit are evenly divided between direct and retrograde motion.