I know the answer, but just so I don't get it wrong on study island:

Since 2006, what has Pluto been classified as in the Solar System?

A.

a meteorite

B.

a major planet

C.

a planetary satellite

D.

a dwarf planet

In 2006, the International Astronomical Union created a new category of object in the solar system. The first object to be listed in that category was Pluto, and several more have been discovered and included since then.

The category is "Dwarf Planet".

(D is the answer and here is why) "Aug. 24, 2006: Pluto Deplanetized. 2006: Pluto, once the ninth planet from the sun, is downgraded to a mere "dwarf planet." Our solar system loses a favorite kid brother and now has, officially, only eight planets."