Which two of these events directly led to the beginning of European exploration?

How should the student cite this source using mla citation format?

The fourteenth amendment how did the action resolve a longstanding conflict in post-civil war america? it defined the process for readmittance of the former confederate states into the united states of america. it ensured the right to vote to all male citizens of the united states, regardless of race, color, or prior servitude. it defined citizenship and related rights for african americans. it abolished slavery in the united states.

What from the columbian exchange had perhaps the biggest impact on the world?