The Earth itself is a source of terrestrial radiation. Radioactive materials including uranium, thorium, and radium exist naturally in soil and rock. Essentially all air contains radon<span> , which is responsible for most of the dose that Americans receive each year from natural background sources.</span>
The answer would be C. velocity. When white light enters a prism it is refracted. This refraction is caused due to a change in velocity (generally speaking, velocity is considered speed in some cases) when entering the prism. In other words, when light enters a prism at an angle, the glass slows down the light causing the light to split into different colors.
Answer: b or c
Explanation: on khan academy
