The Great Wall is a fortificated East-to-West line which historically has delimited the Chinese Northern border. Its primary purpouse was to defend the Chinese territory against the invasions and quick raids organized by the nomadic people from the Eurasian Steppe lands, located more to the North.
But rather than as a fixed border, it should be regarded as a transition zone which establishes a distinction between two different lifestyles, even nowadays: the farmer regions in the South with sedentary ways of life and the pasture lands in the North, where its inhabitants have nomadic lifestyles and work mainly in animal husbandry activities.
The unemployment rate greatly increased due to Great Depression which was caused by people buying items on credit and an economic downturn caused by bank failures and the stock market crash.
I assume this is split into four choices. Then it's the second one.
Average number of people in a given area.
The League of Nations was created AFTER WW1, so it had no effect on WW1. It was cloaked in the name of preventing another World War, but its main purpose was to enforce the Treaty of Versailles.