What does b.c.e , mammoth , mastodon camel and sloth mean in the passage?
Between 11,000 and 10,000 B.C.E., North America was populated by a wide variety of great beasts, like mammoth and mastodons, both elephant-like creatures with big tusks, and camels, giant sloths, the list goes on.

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Answer

B.C.E. (= B.C.) stands for "Before the Common Era." C.E. (= A.D.) stands for "Common Era."

Mammoths, mastodons, camels, and sloths are the "great beasts" (animals) mentioned in the sentence. You can search for them on the internet to learn more about each animal.