The big bang theory states that the universe began with a gigantic explosion
a. 4.4 billion years ago.
c. 50 billion years ago.
b. 10 to 20 billion years ago.
d. 100 billion years ago.

B. 10 to 20 billion years ago.

Explanation:

The Big Bang theory is the dominant cosmological model of the observable universe. This model explains that the universe began to expand from a “point” (often called singularity) of a very high-density and temperature, and from that point, for what is believed to be a time lapse of approximately 13.8 billion years, the universe has continued expanding and evolving. This model is still prevailing because through it, it is possible to explain a large range of observable phenomena in the universe.  

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