Which two statements are true about analog to digital conversion of voice signals for use in digital telephony networks？ （）

• A、 The three required steps in the analog to digital conversion are sampling， encoding， and compression.
• B、 The three required steps in the analog to digital conversion are sampling， quantization， and compression.
• C、 The three required steps in the analog to digital conversion are sampling， quantization， and encoding.
• D、 The output of the sampling process is a pulse code modulation （PCM） signal.
• E、 The output of the sampling process is a pulse amplitude modulation （PAM） signal.