For the time signal, please select the correct answers in the following statement.

A、Acontinuous-timesignalmustbeananalogsignal;
B、Adiscrete-timesignalmustbeadigitalsignal;
C、Ananalogsignalmustbeacontinuous-timesignal;
D、Adigitalsignalmustbeasignalwithdiscrete-valuedamplitudes