In Which policy demonstrated America's increased interest
internationalism after World War II?
A. imposition of tariffs on imports
B. the Marshall Plan
C. the Neutrality Act of 1935
D. refusal to sell military supplies to belligerents
E. the Monroe Doctrine

I believe that it is B

Why? The Marshall Plan was an American initiative passed in 1948 for foreign aid to Western Europe. The United States transferred over $12 billion in economic recovery programs to Western European economies after the end of World War ll.

Also you can do process of elimination and say
A makes no sense
C is prohibiting the export of “arms, ammunition, and implements of war” from the United States to foreign nations at war
D again really makes no since
E was put into law by our 5th president in 1823 (World War 11 happened in the 1940s)

So it has to be B

Hope this helps :D