Answer:
A) Alliance members signed treaties to defend each other in times of war.
Explanation:
As the alliance members signed the treaty to defend themselves in times of war, and the Entente members also did the same, other little countries also signed treaties of defense and alliance, this rose up tension when archduke Francis Ferdinand from austria was assasinated by Serbia made that several allies, joined the war since Serbia was allied to the entente and Austria to the Alliance, this was the start of WWI.