I think it was because we really don't know what exactly happened in the past.
Also, I'm pretty sure people did not keep track of colored people back then.
The answer is: A. Tobacco cultivation
Since this happen prior to industrial revolution, production for almost all products is being done with large number of manual labors. Tobacco was a very hot commodity at a the time since the health risk was still unknown. Slaves would provide large amount of manual labors with very cheap price for the plantation owners.
Only thing I can think of is ivory. They do produce it, it is exported but that's illegal...
Answer:
Because there is a mix of underage and of age students on campuses, the alcohol flows rather freely. If the drinking age were to be raised to 25, most students on campus would be underage, and as some hope, it could curtail the excessive drinking and resulting negative consequences.