@rust96 @Gnorian @RedemptionBoots : Practice and with time the listening skills will develop. Other than that you should know that 'Junge' is masculine = der Junge, and because of the possessive determiner 'mein' this is mixed inflection and the -r from the "der" gets attached to the klein, thus resulting kleiner.
See here German adjectives: http://en.wikipedia.org/wiki/German_adjectives
The nominative masculine form of an adjective after a possessive adjectivehas an "-er" suffix: it is the mixed inflection https://en.wikipedia.org/wiki/German_adjectives#Mixed_inflection
Nominative case, masculine, mixed inflection. -er ending.
See this chart. Maybe read the whole page.
Hope that helps!
A little trick my teacher told me. If the article preceding the noun you have the ending that defines the gender (eine, der, das etc.), in the adjective use the ending corresponding on the table of weak inflection. Otherwise put that ending to the article. Example: Mein kleiner Junge. Der kleine Junge. Ein rotes Fleisch Das rote Fleisch. Ich habe einen roten Apfel Ich habe ein weisses Pferd
Not that I would translate it this way normally, this was purely for testing, but why would you list 'dude' as a possible translation of 'Junge' if when put into this sentence, it then marks it incorrectly? Otherwise I don't see the point in listing a 'viable' answer that you then don't mark as viable. Needs adjusting