*Question E4E10:
Which of the following can create intermittent loud roaring or buzzing AC line interference?*  

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

### AI Response: (may contain errors)  

To understand why the correct answer is "All these choices are correct," let's break down each option and how they can create intermittent loud roaring or buzzing AC line interference.

1. **Arcing contacts in a thermostatically controlled device**:
   - When contacts in devices like thermostats or relays arc, they can create electrical noise. This arcing generates high-frequency interference that can radiate through power lines and affect nearby radio equipment.

2. **A defective doorbell or doorbell transformer inside a nearby residence**:
   - A malfunctioning doorbell or its transformer can produce intermittent buzzing or roaring sounds. The transformer may create electrical noise when it fails, which can couple into the AC line and cause interference.

3. **A malfunctioning illuminated advertising display**:
   - These displays often use high-voltage components and switching power supplies. If they malfunction, they can generate significant electrical noise, leading to interference that can be picked up by radios.

Since all three options can indeed create such interference, the correct answer is:

**D: All these choices are correct.**

### Why the Other Choices Are Incorrect:
- Each of the other choices (A, B, and C) is not incorrect on its own; rather, they all contribute to the same type of interference. Therefore, selecting any one of them alone would not fully capture the range of potential sources of interference.

### Useful Rules of Thumb:
- **Interference Sources**: Look for devices that switch on and off or have arcing contacts, as these are common sources of electrical noise.
- **Frequency Range**: AC line interference typically falls within the HF (High Frequency) range, which can affect amateur radio operations.

In summary, all the listed devices can create intermittent AC line interference, making "All these choices are correct" the right answer.