Answer:
The sentence in the excerpt that speaks about the purpose of the text is:
(It is the design of this, and of the two succeeding chapters, to describe the prosperous condition of their empire; and afterwards, from the death of Marcus Antoninus, to deduce the most important circumstances of its decline and fall; a revolution which will ever be remembered, and is still felt by the nations of the earth.)
Explanation:
The excerpt begins by establishing a broad view of the Roman Empire’s rise and fall....
“In the second century of the Christian era, the empire of Rome comprehended the fairest part of the earth, and the most civilized portion of mankind. The frontiers of that extensive monarchy were guarded by ancient renown and disciplined valor. The gentle but powerful influence of laws and manners had gradually cemented the union of the provinces. Their peaceful inhabitants enjoyed and abused the advantages of wealth and luxury.”
The conclusion focuses on centuries of the roman empire, this is the reason why the right answer covers both the rise and fall of the Roman Empire.