Answer:
Correct answer is A. used the attack to justify taking aggressive action against Serbia .
Step-by-step explanation:
Option A is correct because after the assassination on June 28th 1914, Austria-Hungary declared war on Serbia on July 28th, starting a great offensive on its western and northern boundaries.
B is not correct as Ottomans entered the war in later stage, and Serbia was not their territory.
C is not correct as Germany stayed on the side of Austria-Hungary.
D is not correct as Triple Entente fought against Austria-Hungary in this war.