Which events sparked World War I? Check all that apply.
The assassination of Archduke Franz Ferdinand angered Austria.
Serbia declared war on Austria, which caused Austria's allies to go to war.
Nationalism increased tensions in the Balkan peninsula.
Russia's mobilization plan called for an invasion of France through Belgium.
Alliances caused a chain of events that pulled each country into war.

The assassination of Archduke Franz Ferdinand.

Explanation:

The immediate cause of World War I that made the aforementioned items come into play (alliances, imperialism, militarism, nationalism) was the assassination of Archduke Franz Ferdinand of Austria-Hungary. In June 1914, a Serbian-nationalist terrorist group called the Black Hand sent groups to assassinate the Archduke.

Nationalism increased tensions in the Balkan peninsula.

The assassination of Archduke Ferdinand angered Austria-Hungary.

Alliances caused a chain of events that pulled each county into war.

Explanation:

b - those executed came from every social and economic class