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.