You are right about the second one, but the first and third answers need to be swapped.
1. Economic - Shortage of domestic goods. A shortage means that there isn't enough of something, relative to the demand for this thing. If the American population suffered from a shortage in goods they used in their every-day life (coal, firewood, some fabrics, shoes...), it is because the economy was focused on the war effort during WWI.
2. Political - Letter bombs sent to public officials. Left-wing radicals referred to as Galleanists (after Italian anarchist Luigi Galleani) sent a series of package bombs to representatives of the political class, law enforcement, business and the media in the late 1910s to protest capitalism in the United States. These bombings were therefore politically motivated.
3. Social - Race riots in northern cities. Issues which deal with race relations are a society concern, that is why it is the "social" problem here. The need to produce war materials, as well as the hope for a more tolerant society than in the South, led many African-Americans to migrate northwards during the war. When the war ended, racial tensions increased because the inhabitants of northern cities found themselves competiting against one another for jobs and homes.
