According to Democritus' atom theory, everything in the universe is made of what?

Democritus' atom theory posits that everything in the universe is composed of atoms, which are indivisible and fundamental building blocks of matter. His philosophical perspective was groundbreaking for its time, suggesting that all physical substances are made up of tiny, indivisible units that differ in shape, size, and arrangement. This idea laid the groundwork for later scientific developments in chemistry and physics, cementing the concept of atoms as the essential components of all matter.

In contrast, the other options like elements, molecules, and particles, represent broader or different categories related to matter. Elements are pure substances consisting of only one type of atom, while molecules are made from two or more atoms bonded together. Particles is a more general term that could refer to various small units of matter, including atoms and subatomic particles. However, it is specifically the idea of atoms that is central to Democritus' theory, distinguishing it as the most precise answer.