A. They were trying to find a trade route to make trading easier, so they explored a whole lot more.
B. The Colombian Exchange contributed to the rise of slave trade because when they picked up goods, they just piled 100 or so slaves in the bottom deck. Once a few people had some, many others began to want them and supply and demand skyrocketed. It was easy because the slaves had a different skin color and spoke a different language. The Europeans did not see them as people.