The answer is B. A guitar generally produces sound waves that propagate when the strings are strummed. The strings are displaced through the vibrations caused by contact of the hand and the guitar. You will also notice the vibrations by looking closely to the string. Wave particles continuously collide with each other to make a sustaining or prolonging sound.
A guitar produces sound wave particles, which move and displace one another. A microwave oven, a light bulb, and a radio have electromagnetic waves, which do not displace one another.
