Pluto Was Discovered in 1930, Becoming the 9^th Planet in the Solar

Pluto was discovered in 1930, becoming the 9^th planet in the solar system. As telescopes improved, other Sun-orbiting objects were discovered. Some of those were even larger than Pluto. By 2005, it was becoming apparent that many more objects would soon be discovered and that the number of planets in the Solar System could swell to as many as 50. After much debate, scientists in the International Astronomical Union (IAU) concluded that Pluto and the other similar celestial bodies orbiting the Sun should be classified as "dwarf" planets. Since a "planet" must clear the space surrounding its orbit, our Solar system now has 8 planets.
-Why weren't the other Pluto-like objects discovered earlier?

A) Scientific explanations are tentative.
B) Scientific hypotheses are falsible.
C) Scientific explanations make predictions.
D) Science is limited by technology.