Which three are supervisory signals? (Choose three)

A.
busy

B.
on hook

C.
off hook

D.
call waiting

E.
ring

Explanation:

1.SupervisorySignalling- electrical voltages and tones that can be heard are used to signify call status as follows:
2.1.On-hook- produces an open circuit which does not allow anysignalling, only the ringer can operate.
2.Off-hook- lifting the handset closes the circuit and allows the telephone switch to send an audible dial tone to the receiver.
3.Ringing- the switch sends a ringing voltage to the destination telephone as notification of an incoming call.
Also an audible ringing tone is sent to the caller telephone to indicate that the call is progressing. This tone takes the form of a pattern calledCadenceIn Europe this Cadence takes the form of a double ring (duration of 0.4s separated by 0.2s) followed by two seconds of silence, whereas in theUSit takes the form of two seconds of ring followed by four seconds of silence.