For this item, I think the answer is letter "B. spreading religious beliefs to new areas and cultures". The word diffusion positively means the movement of from one area to another place where there are very few people with the same religion.
B.) spreading religious beliefs to new areas and cultures.
Explanation;
-Cultural diffusion is the spread of cultural beliefs and social activities from one group of people to another.Through cultural diffusion, horizons are broadened and people become more culturally rich.
-Cultural diffusion is important to the development of culture because it allows cultures to improve based on what they learn from the others. Cultural diffusion can lead one country to influence another's culture through trade, travel, or immigration.