Translation:I will live in Berlin for a year.
I think that that alternative is inconsistent with much of the rest of the course and I would not have added it myself.
If you prefer, I'll remove it, for consistency.
Or perhaps the whole sentence should be removed; as I said elsewhere, I don't think that für ein Jahr is good German.
You've noted on the reverse sentence that there are other errors there as well (English "I" instead of German "Ich" in most of the accepted alternatives).
This is a very old exercise that has not been touched for four years, as far as I can tell.
What's wrong with what?
We can't see what you saw, what you typed, or what the system might have suggested as a correction, so any references to "it", "that", "the sentence", etc. are fairly useless.
Please quote the entire sentence you are referring to, even (or especially) if you're asking about a single word. Thank you.