Question

what was discovered in 1965 and is believed to be leftover thermal energy from the big bang?
red shift
the eagle nebula
the doppler effect
background radiation

Explanation:

In 1965, Arno Penzias and Robert Wilson discovered cosmic microwave background radiation, which is thought to be leftover thermal energy from the Big - Bang. Red - shift is related to the expansion of the universe and the Doppler effect is about the change in frequency of waves due to relative motion. The Eagle Nebula is a star - forming region.

Answer:

background radiation