Answer: D. Dwarf Planets
Explanation:
Dwarf planets have round shape and orbit the sun. They do not clear their orbits due to smaller gravitational pull and hence, cannot be classified as a planet. A dwarf planet may or may not have moons. Dwarf planets are smaller in size than planets.
Pluto was once classified as planet but was demoted to dwarf planet as many other similar sized objects were found in its neighborhood in Kuiper belt (Eris, Haumea, Makemake) . One dwarf planet is present in asteroid belt as well. It is the largest object in the asteroid belt.
