Which planet is outside of the solar system?

A. Earth

B. Asteroid belt

C. Sun

D. Nebula

The answer would be D.) Nebula

D. Nebula

Remember that the sun is in the center of the solar system.

The earth is the planet on which humans inhabit, and we orbit around the sun.

The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars and Jupiter.

Using this info, we only have D. left.