A supersonic plane flies at the speed

Explanation

### Step-by-Step Solution:

1. **Understanding Supersonic Speed**:
- A supersonic plane is defined as an aircraft that travels faster than the speed of sound. The speed of sound varies depending on the medium (air, water, etc.) and conditions (temperature, pressure), but at sea level under standard conditions, it is approximately 343 meters per second (or about 1235 kilometers per hour).

2. **Characteristics of Supersonic Planes**:
- Supersonic planes can travel at speeds greater than the speed of sound. This means they can reach speeds of over 343 m/s (or 1235 km/h). The term "supersonic" indicates that these planes can break the sound barrier.

3. **Sound Propagation**:
- When a supersonic plane flies overhead, it travels faster than the sound waves it generates. Consequently, the plane will be seen and heard at different times. The plane passes by before its sound reaches the observer, which is a unique characteristic of supersonic flight.

4. **Identifying the Correct Option**:
- Given the options provided in the question, the correct choice would be the one that states the plane's speed is greater than the speed of sound. This aligns with the definition of a supersonic plane.

5. **Conclusion**:
- Therefore, the specialty of a supersonic plane is that it flies at a speed greater than the speed of sound, which allows it to create a unique experience for observers on the ground.