They do not fight.
= 그들은 싸우지 않아.
= 그들은 싸우지 않습니다.
= 그들은 안 싸워.
= 그들은 안 싸웁니다.
Does DuolingoI accepts them all as correct?
It doesn't accept 안 싸워요 which I guess makes sense in the context of this lesson but still
Why can I not say 그들은 싸지 마 ?
I guess it would be 싸우지 마 because the verb is 싸우다.
But that's not correct here because it's a command like "Don't fight"