Answer:
the more accurate and better phrase, I think, would be option B.changes in US economy after World War II
Step-by-step explanation:
option A. can include the changes the States had during the war too.
option C. does not point out to the changes in US
option D. includes comas which is not really in the form of a real command. a query for search must not include these characters, though you may get the result at times.
so I think the right answer would be option B.