Answer:
The right choice is:
They feared that the United States would be drawn into costly foreign wars.
Step-by-step explanation:
Isolationism has been popular in different periods of American history. After WWI, many Congress politicians and a large part of the public did not want to see the USA engaged in foreign commitments that could drag it into wars in other continents. Thay´s why the US didn´t ratify the Treaty of Versailles and declined to make part of the League of Nations.