Is bánh mỳ an accepted alternate spelling of bánh mì? The multiple-choice question only listed Cái bánh mỳ as an answer, but that spelling hasn't been used before.
I don't understand why bánh mì is an acceptable translation for "the bread", while in other places, there has to be a classifier before the noun to convey definiteness. Why, for instance, in other places in this course, chim sẻ is not enough for "the sparrow" and a con has to be added, while here it doesn't seem to matter if I use cái or not.
I think that is a problem of Duolingo in general. The Japanese lessons I used additionally to a language course there also didn't use the proper classifier at all times and the translations were way more specific than the actual sentence. My best guess is that Duolingo simply didn't come up with/ just didn't use a better translation for the words on their own without classifiers and acts as if it was the same
Ổ is a rare classifier (it is, i think?) that is only used for a few thing, so you could just try to remember them.