Federal Bureau of Investigation:

The FBI is organized into functional branches and the Office of the Director, which contains most administrative offices. An executive assistant director manages each branch. Each branch is then divided into offices and divisions, each headed by an assistant director. The various divisions are further divided into sub-branches, led by deputy assistant directors. Within these sub-branches there are various sections headed by section chiefs. Section chiefs are ranked analogous to special agents in charge.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Who heads an office or division?
an assistant director