Answer:
The correct answer is option D, continue to expand and cool
Step-by-step explanation:
The concept of expanding universe was first time discovered by Einstein's theory . The solutions obtained through his relativity theory has red shifting of light when they come from distant objects travelling all through the expanding universe. Further in 1929, it was proved by Edwin Hubble that universe is expanding when he plotted the curve between the red shift against the relative distance.
Form this it was further linked that due to expansion of universe there can be effect of red shift in the spectrum of the light as the wavelength would have become longer than earlier which would lead to decrease in temperature associated with spectrum and thus the universe keep on cooling continuously as it expands continuously.