All the given factors are responsible for unemployment in the U.S. declined and the gross national product increased during World War II.
Option: D
Step-by-step explanation:
There was a desperate need for military personnel and wartime necessities due to the rising demand for greater war production on the home front, labor mobilization under state mandate achieved a new high for Americans throughout World War II.
In this struggle for limited human resources, the government crafted strategies to meet the armed forces and the economy's numerous and overlapping demands for manpower. The manufacturing industries were ordered to provide military tanks and trucks, which raised huge employment and opportunities to structure new business for war reasons as well as to streamline the process owing to their overall participation due to the wider availability of personnel.