Translation:Natura este cel mai bun profesor.
invățatoară also means teacher, yes? But, it is not accepted.
Why "invacatoare" is incorrect? It's also translated as teacher, I guess.
'învățător/învățătoare' is mostly used to refer to a particular kind of teacher, a primary school teacher. 'Profesor' has a more general meaning, but you can't use it to refer to a primary school teacher.