Prepositions are often used.
"Auf Hals" is definitely for " neck"
"in Hals" is definitely for "throat"
There are expressions that in one language uses one and the other language uses the other. http://dictionary.reverso.net/german-english/Hals
There are also other German words for both. http://dictionary.reverso.net/english-german/neck http://dictionary.reverso.net/english-german/throat
Actually it favors "cervix" which is a pretty common problem with pregnant women. I have no idea why duolingo offers us three translations if we can't use them all. I've found another word for cervix (der Gebärmutterhals) and I believe everyone (who needs to use it) uses it. Can anyone explain this duolingo nonsense?
For throat, it will usually be "ln Hals" or "Rachen" or "Kehle" I think to avoid confusion, because you normally talk about the size of a neck rather than throat, you would have to use a different word for this "Ihre Kehle ist kurz." Really though, how can your throat be short and not your neck? There are some expressions that in English "throat" is used but in German "Hals" is used. http://www.reverso.net/translationresults.aspx?lang=ENdirection=english-german