The way I would explain it is quite difficult to understand, so this is what Google says. "The wavelength (or equivalently, frequency) of the photon is determined by the difference in energy between the two states. These emitted photons form the element's spectrum. The fact that only certain colors appear in an element's atomic emission spectrum means that only certain frequencies of light are emitted." I hope this helped.
Answer:
The exhaust system of the car is the excretory system that removes waste.
The gas in the car is the digestive system that provides the necessary energy.
Sound travels through gases faster than it travels through liquids
