Answer:
B, A, and C.
Explanation:
Ferdinand's assassination is what caused Austria-Hungary to declare war on Serbia because they thought they had something to do with which they might have. Russia then declares war on Austria because Serbia is their ally. America then enters the war in 1917 (3 years after the war started) because of two main reasons. One is that Germany would attack American submarine bases carrying civilians. The other reason is the Zimmerman Telegram in which Germany would send a message to Mexico saying to attack America cuz they were afraid they were gonna join the war but Britain intercepted the message, showed it to America, and deployed troops to Europe. Brainliest plz