In the U1900 series unified gateway, which of the following descriptions about prefixes is correct?

In the U1900 series unified gateway, which of the following descriptions about prefixes is correct?
A . The prefixes are divided into intra-office prefixes and outgoing prefixes.
B . The intra-office prefix refers to the prefix used when dialing between different extensions of the same company.
C . Since prefix 28 includes prefix 289, the system analyzes the called number according to the maximum matching principle. For calls with the called number 28901111, prefix 28 should be selected.
D . The prefix must correspond to the office route selection code.

Answer: A