The correct answer here is A) Germany was threatening Great Britain and the Soviet Union.
At the Arcadia Conference in January 1942, the argument that persuaded President Roosevelt and Prime Minister Churchill to pursue a “Europe-first” strategy was that Germany was threatening Great Britain and the Soviet Union.
Roosevelt and Churchill participated at the Arcadia conference, Washington D.C. Through much discussion, they considered that the "Europe first" strategy was of the utmost importance because Germany was threatening Great Britain and the Soviet Union. All the war efforts should be focused on Europe first, instead of fighting Japan.