The correct answer is A. it annexed Bosnia and Herzegovina.
Explanation
The Austro-Hungarian Empire was a created European State that existed from 1867 under the "Austro-Hungarian Compromise" until 1919 when it was dissolved, giving rise to the states of Austria, Hungary, Czechoslovakia, Fiume, Slovenia, Croatia, and Serbia.
One of the worst crises that the Austro-Hungarian Empire experienced was the result of Franz Joseph I's decision to annex Bosnia-Herzegovina, on October 6, 1908, which caused the discontent of the Serbian community that instead of calming their separatist spirits, embodied a feeling of enmity against the Austro-Hungarian Empire, which would later be seen in the First World War. According to the above, the correct answer is A. It annexed Bosnia and Herzegovina.