The correct answer is A. It explains that the United States should oppose Hitler even if he declares it an act of war.
Step-by-step explanation
In Franklin D Roosevelt's "Four Freedoms" speech, this president argues why the United States should get involved in the conflict of World War II by providing support to European democracies despite threats from dictators (especially Hitler) in opposition to these actions, as expressed by saying that "This aid is not an act of war, even if a dictator should unilaterally proclaim that it is". According to the above, the theme or idea in the text is A.