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."
No. It is a complete sentence. They (subject) wanted (predicate, with) their own post office(object).
"must report at the office" is the complete predicate of the sentence. It includes the main verb "report" and the prepositional phrase "at the office."
"All visitors to the factory" is the complete subject.
must report at the office
must report at the office
must report at the office
must report at the office
must report at the office
must report at the office
must report at the office
It is not a complete sentence.
This is consider to be a complete sentence. As long as it has more than 3 words correct capitalization and a period at the end.