Why did the United States enter the war on the side of the Allies?

AAustria-Hungary began using zeppelins against American colonies

BGermany resumed unrestricted submarine warfare on Allied shipping

CThe Ottomans massacred tens of thousands of Armenian men and boys

DThe British were in danger of losing their colonies in Africa

I think it's either A or D but I'm note sure which one. I'm not good with history so I could be wrong with either of those choices.