Which of the following was not a cause of wwi? a. alliances b. militarism c. communism d. nationalism

C. Communism 

While (i believe) there were communists during the time, the main cause of WWI was the other 3.

Alliances: because of the assassination of Archduke Ferdinand, Austria-Hungary declared war on Serbia, which sparked the chain of events that led to a global conflict.
Militarism: The build up of arms and armies as well as the conquering and acquiring of new territories led to both sides fighting for the same lands.
Nationalism: Without Nationalism, there would be no support for the war effort, leading to a deescalation of the war.

hope this helps