Answer: Option (A) is the correct answer.
Step-by-step explanation:
Models of solar system has been designed from time to time. The present model of solar system shows that nine planets are orbiting around the Sun.
This model is also known as Heliocentric model whereas it is also shown that only Pluto has different orbit as compared to rest of the planets.
Therefore, we can conclude that the model of the solar system changed, because understanding of the solar system changed.