What happens when the crest of one wave meets the trough of another wave.

Phenomena that occurs when two or more waves of the same type meet up in the same medium at the same time, such that they align crest to trough. When this occurs, the wave energies cancel each out, creating an overall smaller wave at the point of interference.

i think it is d. e because the next one is igneous.

in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.