Cultural diffusion was most advanced by. necessary improvements in medical technology. post-world war ii occupation and education reform. nation rebuilding and multinational organizations. the contact of business people with foreign cultures.

Cultural diffusion was most advanced by the contact of business people with foreign cultures. A and B are definitely not correct as their impact is obviously not as important. C could be correct, but business people are those whom we should thank for today's cultural diffusion. It means that culture is all over the world - people are generally familiar with other nation's culture, and it's all thanks to business people who spread their culture when they go to work in foreign countries.