I suppose you could say:
It's the city I lived in three cities ago.
It's a bit clumsy, but I can't think of a better alternative. It's also informal.
Most of the time we wouldn't express this concept directly, instead saying something like:
That's where I lived six years ago. I've moved a few times since then.
If I wanted to be specific, I might say something like:
I've moved three times since I lived in City A.
Of course, you can come up with variations on these themes.
Absolutely right, A is colloquial shorthand and not grammatically proper. Adding who improves the text but doesn't fix it; there's still an unsemantic tense use. How can you close the curtains if you've already left the office? Both B and C are acceptable and correct remedies.
B indicates you should, as part of the process of leaving, close the curtains.
C specifies that the curtains are to be closed immediately before exiting. The use of present tense tells us that the two actions happen at (effectively) the same time, and logic tells us that the curtains must be closed before you've left. Whether or not closing the curtains is part of the process of leaving is technically ambiguous but irrelevant.
(If you are the last person to leave applies in both cases, obviously.)
You're also spot on with the addition of the; it should indeed read the curtains. Technically speaking, without the it's unspecified which curtains should be closed, though the meaning is readily evident without the article.
Bonus alternative: you might also fix the sentence like this:
Please close the curtains if you are the last one left in the office.
Here, one need not be leaving to be obligated to close the curtains.
Best Answer
The words Final and Last are synonyms. They can be used interchangeably most of the time. But it doesn't mean that both of these words imply the same meaning in all contexts. The context plays a vital role on whether to use Final or Last in a sentence. The word 'Final' implies the only being remaining or ultimate. So, "the final week of staying in this city" suggests that there will be no more weeks for staying in this city or it is the only being remaining week for staying in this city. On the other hand, the word "Last" means coming at the end of a series. "The last week for staying in this city" simply means that this week is the last week of all other previous weeks for staying in this city.
Furthermore, the word 'Final' is more formal than 'Last'. To cut the long story short, Final means 'Last' according to http://dictionary.cambridge.org/dictionary/english/final , Therefore, the former statement implies the letter statement without having much difference between them.