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.
I gave my students this multiple choice question: 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?

Only one answer is correct among these 4 choices:
- 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.

Could you tell me which one is correct?

Classifications change as new evidence is gathered.