The two most important things coming from the New World to the Old World:

what are the options? If it's a extended response. Christopher Columbus introduced horses, sugar plants, and disease to the New World, while facilitating the introduction of New World commodities like sugar, tobacco, chocolate, and potatoes to the Old World. The process by which commodities, people, and diseases crossed the Atlantic is known as the Columbian Exchange.  

Explanation:

a and c?

i think it is a and c