I'd like to know, too! Shouldn't "langit dapur ini kotor" be correct, too?
I saw on a previous question that langit-langit is not actually plural. Langit is sky and langit-langit is ceiling. Is seems that there are words that follow the pattern of duplication but are not actually plural.
Why is 'langit-langit dapur ini adalah kotor' incorrect?
Why isn't jorok in stead of kotor accepted?