Multiple Choice
In the present theory of the Big Bang, what significant event occurred at about 400,000 years after the universe started expanding?
A) The primordial helium in the universe was produced.
B) The universe became transparent to neutrinos.
C) The temperature of the cosmic background radiation had cooled to its present level of about 3 K.
D) The universe became transparent to photons.
Correct Answer:
Verified
Correct Answer:
Verified
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