The main aim was a; the enforcement acts were passed by congress to protect the rights of African Americans.
That is for sure right I believe.
B because during the 1200s and 1300s, the Mongol took over most of Afro-Eurasia. It was unexpected because they were a nomadic group.
A is wrong because serfdom implies the feudal system only seen in Europe and Feudal Japan.
C is wrong because the European Crusaders pretty lost every Crusade to the Muslims. The outcome of the Crusades were Europe's increased interest in Islamic goods.
D is wrong because the Byzantine Christians didn't do the Crusades, the Holy Roman Empire did.