Answer:
B. Very few Roman emperors in the centuries after Augustus were competent rulers; most were insane, greedy, or both.
C. Exposure to diseases from other lands killed many Romans.
Step-by-step explanation:
The Roman Empire started to decline in 200 AD as a result of the corruption in politics. The Emperors were no longer appointed using due process instead, the position of the Emperor was auctioned and "sold" to whoever desired it. The economy began to deteriorate because the Romans splurged a lot of money on unnecessary things. Their love for women (Prostitutes) made them invest a lot of money to organize parties.
Also, the economic growth of the Roman Empire declined as the Romans relaxed in expanding the gold business. They spent a lot of money than they expanded the gold business. Golds with less quality were produced. With the rise of Christianity in the Empire, Emperors were less regarded, and this gradually declined their powers over the people. The Roman Empire finally collapsed in 476 AD.