"There ain't no such thing as a free lunch" expresses the idea that even if something seems like it is free, there is always a cost, no matter how indirect or hidden.
Germany was hit particularly hard during the American Great Depression. The reason being was that America was a major source of loans for Germany's reparations after WW1. When Hitler came to power as the Chancellor of Germany, he incited the entire country into a nationalistic rage and establishing a totalitarian single party state, with the support of the Nazi Party.
The Zollverein was an economic union of 30 states. The correct option among all the options given in the question is option "b". Zollverein is actually a coalition of German states whose main agenda was to manage the tariffs and all the economic policies within the German territories. Later on it expanded to other European countries as well.
