Read these sentences from the text. After Eris was discovered, scientists had to make a decision. Either Eris was the 10th planet in the solar system or it was not a planet at all! And if Eris weren’t a planet, could Pluto be considered one?

Scientists made new rules for what is counted as a planet, and decided that neither Pluto nor Eris qualified.

Based on this information, what did the discovery of Eris make scientists do?

a
The discovery of Eris made scientists rethink the rules for what is counted as a star.
b
The discovery of Eris made scientists rethink the rules for what is counted as a dwarf planet.
c
The discovery of Eris made scientists rethink the rules for what is counted as a planet.
d
The discovery of Eris made scientists add more planets to the group of planets.