I would have thought "a person" could be either "un person" or "une personne" - is the word always feminine?
I checked it in an online dictionary. They only give the female version "une personne" as translation. I guess a person is always female in French.
yes, "une personne, like "une victime" or "une personnalité" are always feminine, even if you are referring to a man.
why can't you use " on mange"
I'm afraid that Duolingo expects that you remain as close as possible to the original version.
Both were said to be wrong!