"There is a dog in a car behind the office."
Translation:خَلْف اَلْمَكْتَب كَلْب في سَيّارة.
Your sentence is actually quite awkward, and sounds like it says "The dog is situated behind the office," when a dog, not being a stationary object, is not really "situated" anywhere.
It'd sound better if "kalb" was indefinite:
يوجد كلب خلف المكتب
There is a dog behind the office/desk.
Anyway, in Arabic, when the subject of a nominal sentence is indefinite, and the object is a prepositional phrase, you invert their order.
- كلب في سيارة خلف المكتب
is not a grammatical sentence in Arabic. But you move خلف المكتب to the start, and it's actually more idiomatic than any variation including words like هناك or يوجد.
My answer was كلب في سيارة خلف المكتب and it is marked wrong. Is duo getting it wrong here?
Sorry if my answer was confusing. I meant that that sentence is not a grammatical sentence in Arabic, as I stated right after writing it. You need to have the خلف المكتب at the very start for it to work. :)