Final answer:
The minimum sampling rate for a telephone signal at 4 kHz is 8 kHz and for an audio CD at 22 kHz, the standard minimum sampling rate is 44.1 kHz as per the Nyquist theorem.
Step-by-step explanation:
The theoretically minimum sampling rates are based on the Nyquist theorem, which states that to accurately sample a signal, the sampling rate must be at least twice the highest frequency present in the signal. For a telephone signal at 4 kHz, the minimum sampling rate is 8 kHz. For an audio CD at 22 kHz, which is based on the standard of human hearing up to 20 kHz, the minimum sampling rate is typically set at 44.1 kHz to cover the entire audible range and to provide some margin for the anti-aliasing filters that are used in the analog-to-digital conversion process.