*Question G3A11:
How long does it take a coronal mass ejection to affect radio propagation on Earth?*  

*Correct Answer is  D: 15 hours to several days*  

### AI Response: (may contain errors)  

Coronal Mass Ejections (CMEs) are large expulsions of plasma and magnetic field from the Sun's corona. When these reach Earth, they can significantly affect radio propagation by disturbing the Earth's magnetosphere and ionosphere.

### Explanation:

1. **Correct Answer: D: 15 hours to several days**
   - CMEs travel through space at speeds ranging from about 250 km/s to 3000 km/s. The time it takes for a CME to reach Earth depends on its speed. On average, it takes about 15 hours to several days for a CME to travel the approximately 150 million kilometers from the Sun to Earth. This is why the correct answer is "15 hours to several days."

2. **Why the Other Choices are Incorrect:**
   - **A: 28 days**  
     This is incorrect because 28 days is roughly the time it takes for the Sun to complete one rotation on its axis, not the time for a CME to reach Earth.
   
   - **B: 14 days**  
     This is incorrect because 14 days is not a typical time frame for a CME to travel from the Sun to Earth. It is much longer than the usual travel time.
   
   - **C: 4 to 8 minutes**  
     This is incorrect because 4 to 8 minutes is the time it takes for light (or electromagnetic radiation) to travel from the Sun to Earth, not a CME. CMEs are much slower than the speed of light.

### Useful Information:

- **Speed of Light:**  
  Light travels at approximately $300,000$ km/s, taking about 8 minutes to reach Earth from the Sun.

- **CME Speed:**  
  CMEs travel much slower than light, typically between $250$ km/s and $3000$ km/s, leading to the 15 hours to several days travel time.

Understanding these time frames helps in predicting and preparing for the effects of solar activity on radio communications.