A、Cable modems only operate at Layer 1 of the OSI model.

B、Cable modems operate at Layers 1 and 2 of the OSI model.

C、Cable modems operate at Layers 1， 2， and 3 of the OSI model.

D、A function of the cable modem termination system （CMTS） is to convert the modulated signal from the cable modem into a digital signal.

E、A function of the cable modem termination system is to convert the digital data stream from the end user host into a modulated RF signal for transmission onto the cable system.