Choose the correct word/words to complete the following sentence :
When sound travels in a medium ...... (the particles of the medium, the source, the disturbance, the medium) travels in form of a wave.

Explanation

To complete the sentence "When sound travels in a medium ...... (the particles of the medium, the source, the disturbance, the medium) travels in form of a wave," we need to analyze what actually moves when sound propagates through a medium.

### Step-by-Step Solution:

1. **Understanding Sound Propagation**: Sound is a mechanical wave that requires a medium (solid, liquid, or gas) to travel. It travels by causing vibrations in the particles of the medium.

2. **Identifying the Options**: The options provided are:
- The particles of the medium
...