Final answer:
The biggest economic problem facing the postwar United States was inflation, specifically stagflation in the late 1970s. Therefore correct option is A
Step-by-step explanation:
The biggest economic problem facing the postwar United States was inflation.
During the late 1970s, inflation doubled between 1967 and 1973, causing prices to increase while unemployment remained high at 8 percent. This combination of rising inflation and unemployment, known as stagflation, was a major economic challenge for the country.
In addition, the 2008-2009 Great Recession also caused unemployment to rise and incomes to fall, which further exacerbated the economic problem.