Which statements 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 connect directly to a standard telephone， fax machine， or sililar device and supplies ring， voltage， and dial tone
• C、the FXS interface connect directly to an IP phone and supplies ring， voltage， and dial tone
• D、the FXS interface connect directly to ISDN voice channels