"Are those airplanes Russian or Dutch?"
Translation:Azok orosz repülőgépek vagy hollandok?
The problem here is when rearranging Duolingo's choice of selected words we are not given the option of using 'a' (the)
When the adjective precedes the noun, it remains in the singular form, whilst it is in the plural when if follows the adjective. This is a very simplistic explanation, but I'm afraid I can't remember the technical words and terms for a more elaborated answer.