Answer to Question 1
Many Kuiper-belt objects lie in stable orbital resonances with Neptune, as Pluto does. Many Kuiper-belt objects also have the same period and semimajor axis as Pluto. Pluto differs from Kuiper-belt objects in its large size and high reflectivity. However, the high reflectivity can be explained by its large size; as volatile ices vaporize when Pluto approaches the Sun, Pluto's gravity holds them until they refreeze onto the surface. Comets are too small, and these gases escape from their surfaces completely.
Answer to Question 2
D