You should either throw Bosnian out or not offer it together with Serbian. It's a dialect of Serbian really and many people in south Serbia speak the that dialect (see for example Sanjak region: http://en.wikipedia.org/wiki/Sanjak_of_Novi_Pazar). Bosnian language is just a political decision, because it's a sovereign country now and needed to have it's own language as Serbia was an aggressor in the last war, so having the official language named Serbian would offend both Bosniaks and Croats living in the country.

Also, Croatian and Serbian can only be distinguished by words. You can't recognize the intonation because it's the same. If you don't know words specific to these languages, you won't be able to tell the difference.

It would be best to have a filter that prevents them being in the same question.