For the long number and short number service and number mapping for U1900, which of the following statements is CORRECT?

For the long number and short number service and number mapping for U1900, which of the following statements is CORRECT?
A . Number mapping has the highest priority in number conversion.
B . The long number and short number service takes effect only for the calling numbers.
C . The number mapping takes effect only for the calling numbers.
D . When inner users dial "access code 9" + "called number" to place outgoing calls to the PSTN, the outer-office users can be called successfully even without number conversion.

Answer: B