Your best answer is A. The Lusitania was technically a civilian passenger ship, and it was an American vessel (the U.S. had not yet officially entered World War 1). But the Germans knew that Americans were sending weapons to help the British, and the Lusitania was almost certainly carrying weapons for the war in addition to its civilian passengers. The Germans determined that since the Lusitania was probably carrying weapons they were justified to sink it—which they did. Lots of people died, which shifted the political balance back in the U.S. to favor entering the war against the Germans. The U.S. declared war on Germany shortly after.
