"The teddy bear wears green clothes."
Translation:Bamsen har grønt tøj på.
The word "tøj" is uncountable, like "furniture" in English. There is no such thing as a plural version of "tøj".
I assume because the original course designers didn't add it as an alternative, either by design or by oversight. That said, I would probably only add it to appease complaints and only hesitantly, because in everyday Danish no one uses "klæder" to mean "tøj". It is an old word that sounds stilted and formal.