*Question E2A09:
What do the terms “L band” and “S band” specify?*  

*Correct Answer is  A: The 23- and 13-centimeter bands*  

### AI Response: (may contain errors)  

The terms "L band" and "S band" refer to specific frequency ranges used in radio communications.

1. **Correct Answer Explanation**:  
   - The correct answer is **A: The 23- and 13-centimeter bands**.  
   - The L band typically refers to frequencies in the range of 1 to 2 GHz, which corresponds to wavelengths of 30 to 15 centimeters. However, in amateur radio, the 23-centimeter band (1.24 to 1.30 GHz) is often associated with the L band.  
   - The S band refers to frequencies in the range of 2 to 4 GHz, which corresponds to wavelengths of 15 to 7.5 centimeters. In amateur radio, the 13-centimeter band (2.3 to 2.45 GHz) is commonly associated with the S band.

2. **Incorrect Choices Explanation**:  
   - **B: The 2-meter and 70-centimeter bands**:  
     - This choice refers to the VHF (Very High Frequency) and UHF (Ultra High Frequency) bands, which are not classified as L or S bands. The 2-meter band is around 144-148 MHz, and the 70-centimeter band is around 420-450 MHz.
   - **C: FM and digital store-and-forward systems**:  
     - This choice describes types of modulation and communication methods, not specific frequency bands. FM (Frequency Modulation) can be used across various bands, and digital store-and-forward systems are a method of data transmission.
   - **D: Which sideband to use**:  
     - This choice pertains to single sideband (SSB) modulation techniques, which are not related to the definitions of L and S bands. Sideband usage is more about modulation methods rather than frequency bands.

3. **Useful Information**:  
   - Remember that frequency bands are often designated by letters (like L and S) based on their frequency ranges.  
   - A general rule of thumb is that lower frequency bands (like L and S) are used for different types of communication, including satellite and radar applications, which can help in remembering their applications in amateur radio.