Concept:Cathode rays are streams of negatively charged particles emitted from the cathode in a vacuum tube.
Explanation:Cathode rays are produced when a high voltage is applied across electrodes in a vacuum tube.
They travel from the cathode to the anode.
These rays are deflected by electric and magnetic fields, showing they consist of charged particles.
Their properties match electrons, not high-energy electromagnetic waves, protons, or neutrons.
Therefore, cathode rays are simply fast-moving streams of electrons.
Answer:D. Streams of electrons.