Why Ser and not Estar?
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.
Why is there no personal 'a', like 'a mi maestra'?
That's used for when something is being given or done to a person.
Why can't the ella be skipped?
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.
It is a sub!!!
Why is there no personal "a" as "a mi maestra"?
"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
maestra is a female teacher
profesora should be allowed to be used instead of maestra