Modem is a device which performs

Options

A. modulation
B. demodulation
C. rectification
D. modulation and demodulation

Explanation

### Step-by-Step Solution:

1. **Understanding the Function of a Modem**:
- A modem is a device used in communication systems to facilitate the transmission of data over various media.

2. **Modulation and Demodulation**:
- The primary functions of a modem are to modulate and demodulate signals.
- **Modulation**: This is the process of converting digital signals (data) into analog signals (radio waves) for transmission. It involves adding information to a carrier signal, which can be either electronic or optical.
- **Demodulation**: This is the reverse process where the modem converts the received analog signals back into digital signals.

3. **Summary of Modem Functions**:
- In summary, a modem performs two main tasks:
- **Modulation**: Converts digital data into analog signals for transmission.
- **Demodulation**: Converts received analog signals back into digital data.

4. **Conclusion**:
- Therefore, a modem is essential for enabling digital devices to communicate over analog communication channels.