"Nature is the best teacher."

Translation: A natureza é o melhor professor.

[r_i_l_e_y]

If "natureza" is feminine why is the masculine "professor" acceptable? Shouldn't "professora" be the only acceptable answer?

[Paulenrique]

Again we have general sentences. "A vida é o melhor professor" In general sense we use the masculine form.

[unomundo]

But the "correct" answer is given as both forms.

[TobyBartels]

Why are both versions correct? Do they have slightly different meanings maybe: one more specific to nature, one more generally about teachers? (but I'm not sure how to make sense of that difference).

[PhillipBro6]

Is "the best" always "o melhor" or does it change to fit the gender ?
Ele é o melhor professor.
Ela é a melhor professora.
For some reason I thought it was a fixed phrase. O melhor

[Paulenrique]

It changes according to the noun: o melhor, os melhores, a melhor, as melhores.

[CarloGamag1]

Is the article necessary?