RonaldDeVous is right
Pluto is considered a dwarf planet but that doesn't mean it belongs to the class known as "planets." Planets differ in that they have cleared their orbits of debris, or what astronomers call planetesimals. In contrast, dwarf planets are objects that orbit stars or star remnants and are not massive enough to create nuclear fusion or clear their orbits or debris.
Several know and named objects are known to be dwarf planets. On of them is Ceres (named after the Roman goddess of fertility) and it orbits within the asteroid belt. Many more objects in our planetary system are dwarf planets, most of them are yet unknown and unnamed.
If you ask me, this whole classification thing is confusing. Take dwarf stars for example. Half of this class of astronomical objects are true stars that have nuclear fusion (our sun is a "yellow dwarf"). Others are star remnants (white and black dwarfs) and one is a sub-stellar object (brown dwarf).
I just thought that including Pluto in this quiz without including other dwarf planets while calling it a "planet" would creat more confusion.