Throughout most of the 1800s, the most widely accepted atomic theories were based on research performed by an English chemist named John Dalton. The main tenets of Dalton's theory were: Elements are made of tiny particles called atoms. Atoms cannot be divided into smaller particles. All atoms of a given element are identical. The atoms in one element are different from the atoms in another element. A chemical reaction is a rearrangement of atoms. Then, in 1897, while studying electric discharges in a cathode-ray tube, a British physicist named J.J. Thomson discovered electrons. Which tenet of Dalton's atomic theory did Thomson disprove? A. Elements are made of tiny particles called atoms. B. Atoms cannot be divided into smaller particles. C. The atoms in one element are different from the atoms in another element. D. All atoms of a given element are identical.