Which statement is true about Foreign Exchange Station （FXS） ports on a router？（）

• A、The FXS interface allows an analog connection to be directed at the public switched telephone network （PSTN’s） central office.
• B、The FXS interface connects directly to a standard telephone，fax machine，or similar device and supplies ring，voltage，and dial tone.
• C、The FXS interface connects directly to an IP phone and supplies ring，voltage，and dial tone.
• D、The FXS interface connects directly to ISDN voice channels.