Which planet is part of the solar system?

Pluto is recognized as a part of the solar system. It is classified as a dwarf planet and is located in the Kuiper Belt, a region beyond Neptune that is populated with many small celestial bodies. This classification confirms its status as part of our solar system, making it the correct answer.

The Moon, while an important celestial body related to Earth, is a natural satellite rather than a planet. The Sun is a star and serves as the center of the solar system, but it does not fall under the category of a planet. Therefore, identifying Pluto as part of the solar system accurately reflects its classification among celestial bodies.