Why not: a neighbor is tired?
Long story short: the sentence "a neighbor is tired" is almost impossible to make in Arabic. Basically, a sentence with "X is Y" where X is indefinite is not common and difficult to make in Arabic.
There's no period so it's not a sentence.
I had the same question... Why not???
AmineHadji gave a good explanation. Also it's not a sentence if there's no period on duolingo.
how would you say " a neighbor is tried"