The best explanation for how humans populated the earth is they migrated from asia to other continents over the last two million years. they migrated mostly over land from africa over the last eighty thousand years. they developed varied human species in different places over millions of years. they traveled by boat from africa to other continents over the last forty thousand years.

gold discovery in california, and pioneer settlers were sometimes pulled west because they wanted to make a better living. others received letters from friends or family members who had moved west. these letters often told about a good life on the frontier. the biggest factor that pulled pioneers west was the opportunity to buy land.

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option c

explanation:

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