어법상 틀린 부분을 고르는 문제입니다 정답과 설명좀 부탁드립니다

pluto is the god of the underworld in roman mythology . in science, pluto is a tiny body in outer space.
it orbits the sun at the edge of our solar system. it ①used to be considered a planet.
however, new research② has changed this idea. pluto is no longer③ considering a planet. now it is ranked
as an asteroid. it ④belongs to the kuiper belt asteroid group. asteroids are as dense as planets. they also
do not have moons ⑤orbiting around them.