Answer:
Bering land bridge
Explanation:
There is a land bridge theory that states that Native Americans orginally crossed over to North America via a land bridge that connected what is now modern day Russia to what is modern day Alaska.
Existence of sharp economic differences between social classes
The drug that extracted from coca leaves and became a component of coca cola until 1903 was: Cocaine
Back then we still haven't aware of the addictive and destructive nature of cocaine and cocaine can still be sold legally from medical stores. After 1903, we aware of these nature and all of its usage became federally regulated.
I think A. would be the best answer