Answer:
Option D, decline in the coal industry, is the right answer.
Step-by-step explanation:
The United States underwent some significant economic growth in the period after the Second World War or during the Cold War. The postwar period brought prosperity to the United States and made it the richest country in the world. During this time, the GDP of the United States increased remarkably. There were a number of factors responsible for the economic boom in the United States such as the automobile industry, a housing boom and the rise in defense spending. Besides this, funds from the government, a boom in international trade and the readiness of Americans to spend and consume were also some significant reasons for the economic boom. However, decline in the coal industry, did not contribute in any form to the economic boom.