The city had once known____.
A: a prosperity B:the prosperous C:the prosperity D:prosperity.
The first, the B is wrong. The D I think is also wrong. Between A and C I think should use art. 'the', so in my opinion the C is right.
Am I right? Thanks everyone.
Nope. Sorry, Soochu. (D).

'The city had once known prosperity.' We are speaking generally about an uncountable concept: 'I like tea'; 'Money is important'; 'Bigotry and hate cause war'.

You got trapped in the trick. "Known" here works as not a verb but an adjective to mean "well-known"/"well recognized". "Had" here means "possessed"/"owned". "The city owned once well-known prosperity"

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Think again, Paco. This is past perfect of 'to know', in the sense of 'to experience'.

Thank you for the advice. I've heard for the first time "know" can mean "experience" or "undergo". So I surveyed my OED and learned the verb is indeed sometimes used in that sense. But if it is so, why is this sentence in the past perfect tense? I mean it would be enough just to say "The city once knew prosperity". Don't you think so?


[PS] I've found some Chinese people did the same discussion on a web forum for English learning. If you have any interest please visit there.
CLICK HERE: [url="http://bbs.chinadaily.com.cn/forumpost.shtml?toppid=96909"] had known prosperity[/url]
A very silly site, Paco, and I would suggest that you stay far, far away from it; I shall. The discussion went on much too long, and 'China Daily' evidently has no authorities to moderate. That thread was primarily a long argument between H. Norman (who is very wrong) and Temico (who is right, at least on this sentence)-- and then it degenerated into name-calling! I am certainly glad that we do not operate that kind of site here. Such silliness is quickly moderated here, and any personal attacks are deleted immediately.

Thank you for warning me, however-- if I ever see 'China Daily' quoted as a reference, I will ignore it completely.

As to your question, placing 'know' into the past perfect tense is perfectly fine, as is casting it in the simple past. Both are grammatically possible. However, we cannot decide that 'it would be enough just to' use the simple past, without knowing the context. In this case, the past perfect stresses the former state, and if we had the rest of the text, we would likely see that it is being more directly and more effectively compared to the city's poor condition now by using the past perfect.
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OK I understand what you are saying. Yes it could be right to use past perfect tense in a context like as follows.
"In 1895 Sven Hedin visited a city in Taklamakan Desert. The city had once known prosperity."

I got it. Thank you.