"Downtown" is not a term used in UK, unless singing the song by Petula Clarke. We call it Town Centre or City Centre, and signposts will be marked in that way.
Why not "in downtown" the exercise says "i sentrum" i = in. Right?
"in" is only used with "downtown" in English when it's followed by the city: it's in downtown New York.
In the UK we refer to the city center ac central. So can I say "The palace is in central?"
Why is the answer in the indefinite form, i.e. not "sentret" or "sentrumet"?