Translation:They are wearing their little black hats.
Yes, they sound exactly the same and you are not supposed to hear any difference. That means that you can translate by "leur petit chapeau noir", in singular, because in French a plural subject (like Elles here) can have a singular object, not only to mean that there is only one hat for all (which is not the case here, but think about a bigger object: Elles viennent avec leur voiture) but as it is the case here, to mean that these women each have one hat. In English, the plural form is preferable, as far as I know.
When it comes to "elles portent", it cannot be a singular, since the possessive pronoun is "leur" which indicates a plural. In the singular form, it would be "elle porte SON petit chapeau noir".
You are right, there is no difference at all between singular "elle porte" and plural "elles portent".
Duo has implemented a system of recognition of homophones for dictation exercises, and many are already cleared.
However, since all verbs from the 1st group (infinitive in -er, except "aller"), share the same issue of homophony between: 'il Verb-e' vs 'ils Verb-ent' and 'elle Verb-e' vs 'elles Verb-ent', it may take a little while until all case have been covered.
Thanks for your patience.
The correction of my sentence was not correct. I wrote: "Elles portent leurs petits chapeaux noir." The correction was "you incorrectly used the plural of hats, but should have used singular." All else was correct. Since the subject was plural and the possessive and descriptive adjectives were plural, why would use the singular of hat? Not adjudicating, just trying to understand. Tom M.
There is one plural form you cannot miss: "leur(s)" (several women-owners), which would be "son" in singular (one single woman-owner).
For all the other words of that sentence, they are all pronounced the same and without proper context, you may be overwhelmed in interpretations (is it carry or wear, is the wearer/carrier a woman or several women, are we referring to one hat each or several hats, whose hat(s) is it/are they...?).
Therefore, don't worry, try and memorize the correct answer to your first mistake on every question you fail, they use it again next time you are shown the same sentence.