rtekauer,the machine cannot know whether you might think saying "...at to the right" is correct, so it has to count you wrong and show the correct answer.
I accidentally doubled Dónde yesterday, and missed an easy sentence. Makes you remember to take a second to proofread.
Chemdan, if Dúo was trying to make a complete sentence, yes, but this exercise is likely the answer to a question, in context.
For example, at a medical center, someone asks a desk clerk, "Where is the bathroom?" She/he helpfully points to the correct hallway and answers, "Third door on your right."
I'm having trouble understanding when and how to put certain adjectives. Like in this sentence we say "tercera puerta", with the adjective coming before the noun and retaining its gender. In another sentence we said "primer calle" or "buen restaurante", still adjective first, but without the gendering. And most other times we have adjective following the noun. Is there a rule I should be following, or is this one of those things I just have to feel out?