How would you BEST categorize the position of the United States in regards to foreign policy and the growing threat of war in Europe during the 1930s

a. The United States didn't even have ambassadors in European nations during the 1930s.
b. The United States felt that it needed to be involved in all negotiations taking place between rival European nations during the 1930s.
c. The United States constantly used the threat of war to force their agenda with nations across Europe during the 1930s.
d. The country had returned to a policy of isolationism following World War I, and wanted to concentrate on domestic problems during the 1930s.