What is the minimum number of partitions that must be defined given the dial-plan rules listed below?

* All employees can call local and service numbers.
* Managers can call long-distance and international numbers.
* Executives can call all PSTN numbers including premium numbers.
* Only administrative assistants can call executives.
* Incoming calls can only be routed to phones, not to trunks.

A.
6

B.
8

C.
7

D.
4

E.
3

F.
5