Which best explains why Germany sided with Austria-Hungary following the assassination of Archduke Ferdinand? A. The countries shared a border.
B. The countries had an existing alliance.
C. The countries were blamed for his death.
D. The countries both wanted to build colonial empires.
The correct answer is B. The countries had an existing alliance.
Explanation: Germany and Austria-Hungary were part of a larger alliance system in Europe called the Triple Alliance, which also included Italy. This alliance was meant to provide mutual support in case of war. Following the assassination of Archduke Ferdinand, Austria-Hungary sought to take action against Serbia, and Germany supported this move due to their alliance, leading them to side with Austria-Hungary.