*Question T3B10:
What frequency range is referred to as HF?*  

*Correct Answer is  C: 3 to 30 MHz*  

### AI Response: (may contain errors)  

The correct answer to the question about the HF frequency range is:

**C: 3 to 30 MHz**

### Explanation of the Correct Answer:
- The High Frequency (HF) band is defined by the International Telecommunication Union (ITU) as the frequency range from 3 MHz to 30 MHz. This range is commonly used for various forms of communication, including amateur radio, maritime, and aviation.

### Why the Other Choices are Incorrect:
- **A: 300 to 3000 MHz**
  - This range refers to the Ultra High Frequency (UHF) band, which is not classified as HF. UHF is used for television broadcasting, mobile phones, and other forms of communication.
  
- **B: 30 to 300 MHz**
  - This range corresponds to the Very High Frequency (VHF) band. VHF is used for FM radio, television broadcasts, and two-way radio communications, but it does not include HF frequencies.
  
- **D: 300 to 3000 kHz**
  - This range is equivalent to 0.3 to 3 MHz, which falls into the Low Frequency (LF) band. LF is used for navigation and some long-distance communication, but it does not encompass the HF range.

### Summary:
- HF is specifically defined as 3 to 30 MHz.
- Understanding frequency bands is crucial for amateur radio operators, as it helps in selecting the appropriate frequencies for communication.

This knowledge will aid you in both the exam and practical applications in amateur radio.