Concept:Waves are divided into mechanical waves, which need a material medium, and electromagnetic waves, which can travel through a vacuum.
Explanation:Sound waves are mechanical waves.
They need a material medium such as air, water, or solid to travel.
Sound waves cannot travel through a vacuum.
Radio waves, light waves, and X-rays are electromagnetic waves.
Electromagnetic waves do not require any material medium for propagation.
Therefore, among the given options, only sound waves require a material medium.
Answer:C. Sound waves