Answer:
a
Alliances, Imperialism, Nationalism
b
The system of alliances or the way countries form agreements to help each other, was one of the main reasons that world war 1 broke out.
c
The most direct way nationalism caused World War I was through the assassination of Archduke Franz Ferdinand, who was the heir to the throne of the Austro-Hungarian Empire. Many oppressed Slavic groups in the Austro-Hungarian Empire wanted to form independent nation-states.
Step-by-step explanation: