"She has not been my teacher."
Translation:Ella no ha sido mi maestra.
Both occupations (teacher) and relationships (my teacher) use "ser". I think in this case it's because it's a relationship that "ser" is used.
When introducing someone to your teacher you'd say "Ésta es mi maestra", not está. I figure, anyhow.
I'm assuming they prefer it since there is no context around the sentence that would tell you if it's he or she. It can be but it's probably just for more clarity here.
"Personal a's" are used when the person is the direct object of the sentence. (For example, if you see the teacher, or hear the teacher, or admire the teacher).
Here "teacher" is a predicate noun. She = (or in this case, does not =) teacher.
I wrote teacher instead of professor - and got the answer that "teacher" wrong? though the second answer is "teacher" !!??????
It won't even say the "word" sida when you click on it lol. Kind of a giveaway