What best describes an FXO interface？（）

• A、analog trunks that provide the Survivable Remote Site Telephony (SRST) feature 
• B、analog trunks that provide VoIP gateway functionality 
• C、analog trunks that connect a gateway to plain old telephone service (POTS) device such as analog phones, fax machines, and legacy voice-mail systems  
• D、analog trunks that connect a gateway to a central office (CO) or private branch exchange (PBX)