A simple way to separate a true particle beam from electromagnetic radiation is to check how it behaves in electric and magnetic fields. Cathode rays are deflected by both, exactly as expected for a stream of charged particles, and this deflection is how their nature as electrons was originally established and their charge-to-mass ratio measured. Electromagnetic waves such as visible light or X-rays carry no charge and pass through electric and magnetic fields undeflected. Because cathode rays do get deflected, calling them electromagnetic waves contradicts this basic experimental fact, while the statements about producing X-rays on impact, travelling in straight lines, and being fast electrons are all consistent with their established particulate nature.
Therefore, the correct answer is Cathode rays are electromagnetic waves.