The correct answer is "atrás."
First, try to read the sentence: _____ the hospital is the office. Since this is talking about one location in respect to another, we can infer that the answer is going to have to do with directions.
Then, look at the answer choices: atrás means behind, calle means street, and ubicada means located. If you put these words in the blank and try to read the sentence, "atrás" is the only that makes sense (Behind the hospital is the office.).
