Which of the following best describes the main idea of the passage?

The early 20th century saw a paradigm shift in physics with the advent of quantum mechanics. Classical physics, which had successfully explained phenomena at macroscopic scales, proved inadequate for describing the behavior of particles at the atomic and subatomic levels. Figures like Max Planck, Albert Einstein, and Niels Bohr laid the groundwork for this new understanding, introducing concepts such as quantized energy and wave-particle duality.