Final answer:
Democritus' idea was that atoms are the fundamental units of matter.
Step-by-step explanation:
Democritus, an ancient Greek philosopher, proposed the idea of atoms as the building blocks of all matter in the universe. He believed that atoms were indivisible, solid objects that made up everything around us. His theory was based on the concept that different combinations of atoms result in different properties of matter, such as color, taste, and texture.