The correct answer is Archduke Ferdinand was assassinated, Austria declared war on Serbia, Russia mobilized its forces, Germany declared war on France and Russia, and Britain declared war on Germany.
Explanation
The aforementioned events are part of the European warlike conflict known as World War I, which pitted the triple alliance against the triple entente. The first event that occurred during this war was the assassination of Archduke Francisco Fernando on June 28, 1914, at 11 a.m. in Sarajevo. After this, Austria-Hungary made a declaration of war against Serbia on July 23, 1914. This event caused Russia (allying with Serbia) to mobilize its troops towards the Baltic and Black Seas and the cities of Odesa, Kasan, Moscow, and Kyiv.
In response to Russia's military mobilization, Germany decided to declare war on August 1 and two days later on France (also allied with Serbia).
A day later, the United Kingdom entered the war by declaring war on Germany on August 4, since Germany had attacked Belgium even though it had remained neutral so far.
So the correct answer is Archduke Ferdinand was assassinated, Austria declared war on Serbia, Russia mobilized its forces, Germany declared war on France and Russia, and Britain declared war on Germany.
