The first alternative is correct (A).
Drawing on the experience of World War I, economist John Keynes said that war was good for an economy as countries demanded many arms manufactures, as well as food and fuel. Keynes made this observation by analyzing the American economy, which left the first war as the greatest economic power in the world. The US was the main supplier of weapons and food to European countries during the war.
However, it was not just the United States that changed its industrial plants in favor of armaments manufacturing. Other governments have also done this in Russia, England, Japan and more. The factories of that period became the poles supporting the war.
