What is a sentence for office?
I won't be in the office tomorrow.
It is a fragment as there is no subject. Even if you use it as an answer to a question, it is still a fragment, i.e. "Where is the desk? In the middle of the office." For it to be a complete sentence as an answer to a question, you would need to change the sentence to "It's" or "the desk", "is in the middle of the office."