I'm pretty sure is 2 but count on me but if you have to choose 2
Http://www.dummies.com/education/history/american-history/american-preparation-for-world-war-ii/
You're welcome xP
3. The Seventeenth Amendment altered the process for electing United States Senators and changed the way vacancies would be filled. Under the original constitutional provision, state legislatures filled vacancies when a Senator left office before the end of their term.
I have no clue about the others sorry to disappoint
Answer: A The Mongols struggled to govern such an enormous empire.