During the decade following the second world war, the u. s. national
economy
(a) more than doubled
(b) fell back into depression
(c) suff ered from a decade-long recession
(d) remained mostly unchanged
(e) relied mostly on european loans

During the decade following the Second World War, the U.S. national economy "(A) more than doubled," since World War II along with the New Deal had not only pulled the US out of the great depression--it had made its economy stronger than ever. 

The growth of the empire continued to increase their confidence.