*Question G9C10:
Which of the following can be adjusted to optimize forward gain, front-to-back ratio, or SWR bandwidth of a Yagi antenna?*  

*Correct Answer is  D: All these choices are correct*  

### AI Response: (may contain errors)  

To optimize the performance of a Yagi antenna, several factors can be adjusted. Let's explore each option:

1. **The physical length of the boom (Choice A):**  
   - The boom length affects the overall size of the antenna and can influence the gain. A longer boom generally allows for more elements, which can increase forward gain.

2. **The number of elements on the boom (Choice B):**  
   - Increasing the number of elements typically enhances the forward gain and can improve the front-to-back ratio. More elements can also narrow the beamwidth, which is desirable for certain applications.

3. **The spacing of each element along the boom (Choice C):**  
   - Element spacing is crucial for optimizing the antenna's performance. Proper spacing can improve the front-to-back ratio and affect the SWR bandwidth. Adjusting the spacing can help achieve a better impedance match over a wider frequency range.

4. **All these choices are correct (Choice D):**  
   - Since each of the above factors (boom length, number of elements, and element spacing) can be adjusted to optimize different aspects of a Yagi antenna's performance, the correct answer is that all these choices are correct.

In summary, each of these adjustments plays a role in optimizing a Yagi antenna's forward gain, front-to-back ratio, and SWR bandwidth. Therefore, the correct answer is Choice D: All these choices are correct.