Which of the following descriptions is correct?()

A.In the GSM system, the time diversity is implemented using the frequency hopping technology.

B.In the GSM system, there should be an interval of 3 timeslots for the mobile station to receive and send signals.

C.The GSM system provides encryption measures. The encryption sequence is generated by the encryption key Kc and frame. number through the A8 algorithm.

D.The multiple access mode of GSM is the combination of FDMA and CDMA