Answer:
Option D, red shift in electromagnetic spectrum
Step-by-step explanation:
According to the Big Bang theory the universe is continuously expanding and all celestial bodies are moving away from each other. This fact was established when red shift affect was discovered. A red shift is basically a shift/increase in the wavelength of light released by any star over a period of time. The farther the star, the more is its wavelength red shifted.
This red shift is continuously increasing which means that the light emitting celestial objects are continuously moving away from each other.
Hence, option D is correct answer