"<span>A. It amounted to an informal declaration of Cold War" would be the best option, but it was not even remotely formal--in that it simply said that the US would come to the aid of any countries in danger of becoming communist. </span>
It was mostly "c. The end of the Crusades" that helped to bring about an increase of trade within western Europe during this time, since this period had been previously dominated by mass violence that disrupted trade routes.
I would say c limited slave trade between Africa and the colonies :)
