most world historians would agree that the key to european predominance in the world economy during the nineteenth and early twentieth centuries was:

this question shoud be under spanish category, not

answer is b.

  it is always the best policy to have good communication and good relations between individuals and, specially, between leaders of the countries. for this purpose, among others, there is a common place, the united nations, where the representants can present his and learn about the other country's policies.