It was the difference of views on the matter of slavery. The answer would be b.
If that didn't help, then I apologize.
Answer:
The columbian exchange provided the transfer of goods, diseases, crops, and animals from the new and old world.
This is usually the result of an underdeveloped infrastructure or lack of technological achievements. The communication revolution requires countries to have highly advanced infrastructure that can support making a huge communications web and many countries have historically been destroyed by wars or have generally been poor and couldn't develop in that field, which means that nowadays they can't enter it quickly.
The correct answer is letter D. There was a wave of attacks in Western Europe in the Middle Age which has destroyed almost completely the Roman Empire, and has diminished the population. Even with such attacks Western Europe managed not to fall apart, and the Church had a big role. While the Roman Empire collapsed, the Church took over many government functions. The attacks were protagonized by ostrogoths, visigoths, vandals, vikings, muslims, persians, saxons.
