Earlier scientists did not use appropriate tools. Pluto should not have been classified as a planet. Classifications change as new evidence is gathered. Review of planetary characteristics should occur every year.
Pluto was discovered in 1930 and was named the ninth planet. In 2003, an object larger than Pluto was discovered by astronomer Michael Brown. Pluto has been reclassified as a "dwarf" planet. What does this most likely suggest about scientific investigations?

Options:
- Earlier scientists did not use appropriate tools.
- Pluto should not have been classified as a planet.
- Classifications change as new evidence is gathered.
- Review of planetary characteristics should occur every year.

Classifications change as new evidence is gathered.