*Question E7F05:
How frequently must an analog signal be sampled to be accurately reproduced?*  

*Correct Answer is  B: At least twice the rate of the highest frequency component of the signal*  

### AI Response: (may contain errors)  

To accurately reproduce an analog signal, it must be sampled according to the Nyquist-Shannon sampling theorem. This theorem states that:

- **Correct Answer (B):** At least twice the rate of the highest frequency component of the signal.

### Explanation:

1. **Why the correct answer is correct:**
   - The Nyquist-Shannon sampling theorem specifies that to avoid aliasing and to accurately reconstruct the original signal, the sampling rate must be at least twice the highest frequency present in the signal. This is known as the Nyquist rate.
   - If the highest frequency component of the signal is $f_{\text{max}}$, then the minimum sampling rate $f_s$ should be:
     $$ f_s \geq 2 \times f_{\text{max}} $$

2. **Why the other choices are incorrect:**
   - **Choice A:** Sampling at half the rate of the highest frequency component would result in aliasing, where different signals become indistinguishable from each other.
   - **Choice C:** Sampling at the same rate as the highest frequency component is insufficient to capture the signal accurately and would also lead to aliasing.
   - **Choice D:** Sampling at four times the rate is more than necessary. While it would still allow accurate reproduction, it is not the minimum required rate according to the Nyquist theorem.

### Useful Rule of Thumb:
- Always sample at least twice the highest frequency to ensure accurate signal reproduction and avoid aliasing. This is a fundamental principle in digital signal processing.