Translation:At night, I close the window in my room.
I agree with this too. There are a number of sentences throughout the program where "my" is assumed but it appears nowhere in the Japanese sentence. I know that many time "my" is left out of Japanese when the context is clear, but there is nothing in these sentences to provide the context.
General expression of frustration and suggestion for improvement: Given the built-in vagueness and ambiguity of Japanese, why have students type their translations? Too often perfectly acceptable translations are flagged as incorrect. Why not adopt the Spanish Duolingo method and have multiple choice translations?