The presence of a crossover effect in one's data can usually rule out the influence of which rival hypothesis?

1. he was one of the first europeans to set foot in america. without this period in history, we may have never had immigrants, let alone discovered america.2. the islands were producing far more agriculturally at this time then the mainland, so it make sense that the first african slaves went to hispaniola. the crops that were being grown during the 16th and 17 century in this area were very labor intensive. due to disease and all that, that native taino population on the island was wiped out and it was therefore necessary for the spanish plantation owners to look elsewhere for cheap labor. the beginning of the slave trade comes about after pretty much the same sequence of events everywhere in the americas, just at different times. need for increased labor --> loss of native population from disease --> slave trade3.hernando cortés was a spanish explorer and conquistador who landed on the coast of mexico in 1519. cortés traveled over one hundred miles inland to find the city and claim the empire for spain.that's all i got for