Solution:

A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, the term was used to describe any diffuse astronomical object, including galaxies beyond the Milky Way.

Asteroids are minor planets, especially of the inner Solar System. Larger asteroids have also been called planetoids.

A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail.

A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity is not massive enough to cause thermonuclear fusion and has cleared its neighbouring region of planetesimals.