Energy is the ability to do work so I would say that thermal or heat energy is a type of work. Don’t know if this will work but that’s what I would put.
C. Electromagnetic waves don't always need a medium to travel. Note that they do vary in wavelength and frequency however their speed is fixed. Also, EM waves are always transverse and they consist of vibrating electric and magnetic fields.
The answer is protons and neutrons (C)
