The correct answer is D) there was a series of international crises.
In the years preceding World War I there was a series of international crises.
The world was in turmoil in different parts before World War I. The spark that could have generated an international confrontation could have been anywhere. For instance, there was the Moroccan Crisis of 1905. Or the Crisis in Bosnia in 1908. There was another period of crisis in Morocco in 1911. And what was definitively a most problematic issue was the war at the Balkans in 1912. Let's remember that World War I started after the assassination of Austrian Archduke Franz Ferdinand and his wife, in Sarajevo, on June 28, 1914.