The term used to describe the quantity of matter that a body possesses is mass.
The correct answer is (a.) Hydra. Hydra is not a dwarf planet, instead, it is the moon of the dwarf planet, Pluto. There are only four accepted dwarf planets by the International Astronomical Union which were the Haumea, Pluto, Eris, and Makemake.
If the Earth didn't tilt then we wouldn't have seasons.