"Surely the young men do not live in America?"
Translation:Num iuvenes in America habitant?
When verbs are conjugated in Latin, their endings change according to the pronoun that goes with it. For example, habitat would mean "he/she/it lives." So if the subject of your sentence is "young man" which would be a "he", your sentence would be "iuvenis habitat." If you have a plural subject like "young men" the ending changes to "nt". Your noun changes too in this case from "is" to "es". So your sentence would be "iuvenes habitant." You can sometimes find the verb conjugation charts online that show all the pronouns and their verb endings.
I am struggling to understand Duolingo's mindset regarding the preposition "in". Sometimes, it only wants ablative like in this case, sometimes it substitutes genitive. So, it will use "university of Rome" technically in Latin but translate it "in Rome." So when I type it what it technically said, it is wrong. Anyone have a tip on this?
Cities, towns, small islands (usually have one city or town on them), and some few other nouns (like domus) make use of the locative case. This case for first and second declension nouns does look like the genitive. For nouns that do not fall into the above categories (America does not in this sentence) we make use of in + ablative to represent location