I believe 1 and 4 are incorrect. 4 is quite ridiculous, England won the war and had no reason whatsoever to cede colonies to the Germans. 1 is debatable, but the general consensus is that the Americans joined less to fight the "enemy over there" but rather because they felt threatened by Germany's potential alliance with a powerful Mexico and because of Germany's unrestricted submarine warfare. That said, one could argue that 1, in this case, is correct.
I believe 2 and 3 are correct. The United States did join the League of Nations after the war to prevent another conflict and promote peace (that didn't work too well). The League of Nations of the past could be compared to the United Nations of today. The American troops that arrived in Europe in the year of 1918 did indeed help stem the German advance. At some points arriving at a rate of 10 000 a day, the fresh American troops pretty much were able to swarm the war-weary Germans and kill more than the Germans could replace.
The Open Door policy was drafted by the United States about activity in China. The policy supported equal privileges for all the countries trading with China and reaffirmed China's territorial and administrative integrity.
