Which digital modulation method is used to transmit caller ID information on analog FXS ports on Cisco IOS routers? 

Answer options:

A. DTMF
B. PSK
C. FSK
D. MF
E. pulse dialing

C

Link:-http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/vcr1/vcr1-cr-book/vcr-c4.html