WWI was started because a Serbian nationalist assassinated archduke Francis Ferdinand and acting like a friend who is in a fight Germany jumped in and held Serbia responsible for the assassination starting WWI. The effect s it had on European countries were the collapse of their economies and wanting Germany to pay war reparations mostly to Britain and France totaling to 33 billion dollars this is when the Great Depression started after the stock market crash and the failure of banks.
I'm pretty sure the answer is D "Only Roman citizens were allowed to fish and swim in it" although there is a possibilty of it being B because it was controlled by the Roman Empire.
