Which of the following IOS commands will you use to enable Callback Busy Subscribers?

Which of the following IOS commands will you use to enable Callback Busy Subscribers?

A.
Router(config-telephony-service) # ccbs.

B.
It is enabled by default.

C.
Router(config-telephony-service) # callback.

D.
Router(config-telephony-service) # call-back.