Pluto was once classified as a planet. however, scientists no longer classify pluto as a planet. which is a likely reason for this change?
the original hypothesis about pluto was supported.
no observations of pluto were made in the past.
several planets in outer space were found to be similar to pluto.
there were significant changes in scientific knowledge about planets.

There were significant changes in scientific knowledge about planets.

Explanation:

The International Astronomical Union (IAU) defined in August 2006 that, in the Solar System, a planet is a celestial body which:

1. Is in orbit around the Sun.

2. Has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).

3. Has "cleared the neighborhood" around its orbit.

Among other things, this definition caused Pluto to no longer be a planet, a change from how it had been widely considered until that point.

answer: accepted answer: aquatic animals use the oxygen dissolved in water to carry out respiration. since the amount of dissolved oxygen in water is low as compared to the amount of oxygen in the air, therefore the rate of breathing in aquatic animals is much faster than it is in terrestrial animals.

explanation: