I do not have your choices of "the following" Here are some reasons I learned: Christianity, empire was too big and became hard to manage, there were many nonromans attacking parts of empire- Goths, the emperors themselves were weak or insane intrigue was rampant.
The treaty of Versailles blamed the Germans for causing the war, even though it was the Austrians who started the war. The answer is that the allied powers blamed The Empire of Germany.
The answer is D! I hope this helped you
