Translation:Múinteoir is ea é.
They are all correct, yes. This one here stresses the fact that he's a teacher. Unlike English, Irish doesn't stress words to emphasize them; instead, it rearranges them. So what you have here is the equivalent to "He's a teacher."
Presumably, Duo marks all 3 as correct? - as there's no indication of empashis in the question.
Can someone explain the word order and stress/emphasis, because Duolingo is starting to upset me.
When do I want two “é” in the sentence vs one?
I get corrected sometimes when I write “Is múinteoir é Pól.” Sometimes it’s “Is é múinteor Pól” or “Is é múinteoir é Pól” and I’m having a hard time gauging the meaning and sense of it.