<span>a. the amount of matter in a given volume </span>
radio waves,X-rays,
Explanation:
In order from highest to lowest energy, the sections of the EM spectrum are named: gamma rays, X-rays, ultraviolet radiation, visible light, infrared radiation, and radio waves. Microwaves (like the ones used in microwave ovens) are a subsection of the radio wave segment of the EM spectrum.
The answer is B for sure !